->''When you hear hoofbeats, think horses, not zebras.''
-->-- Common medical saying. In TV Land, it might as well be a nuckelavee.

The meaning of the quote above is that real patients usually have common, boring diseases; so when a patient arrives at the hospital, it's those very same common, boring diseases that doctors should check for ''first'', before even considering the remote possibilities of them contracting something rare and exotic.

On medical TV shows, it's usually the exact opposite: A disease that a real doctor might encounter only once in his whole career, or even dismiss as urban legend, could show up on three different shows if it's sufficiently [[RuleOfDrama dramatic]], and will ''definitely'' show up if it's [[RippedFromTheHeadlines made the news recently]]. The cast usually knows how rare the disease is, and frequently provides a LampshadeHanging of its rarity.

Some of these diseases are:

* [[PlotAllergy Allergies]]: In this case, it's not allergies themselves but the strange things characters are allergic ''to'', [[RuleOfFunny especially in comedies]]. The reactions are also unrealistic, especially in cartoons where an allergic reaction causes the character to instantly puff up like blowfish. In live-action, the amount of swelling typically shown would almost certainly be accompanied by anaphylactic shock and closed airway (a life-threatening condition).
* [[FeelNoPain Congenital Insensitivity to Pain]]: An extremely rare condition, but irresistible to TV writers for both the gruesome results of not feeling pain and its metaphorical implications. Appeared on ''Series/{{House}}'', ''Series/{{NCIS}}'' and ''Series/GreysAnatomy'' (and the Australian hospital drama ''AllSaints''), as well as an inbred family on ''Series/TheXFiles''.
* MunchausenSyndrome‎: Not that common, but the inherent drama of a patient fooling their doctors has made it a staple of TV. The "by proxy" variant where a parent sickens (or even ''murders'') their children for their doctor's attention, is even rarer, more dramatic, and thus more likely to show up on television.
** The "proxy" variant also makes it useful for criminal shows, as it is not only a disease, but a crime. ''LawAndOrder'' has had several, most notably the [[RippedFromTheHeadlines Michael Jackson scandal ripoff]] where a woman has her granddaughter pretend to be a victim of said (alleged) molester on top of [[MoralEventHorizon poisoning her to pretend she has cancer]].
* Infertility: Far more common on TV shows of all kinds than in real life. [[LawOfInverseFertility Almost all TV couples who desire a child have trouble conceiving.]] Even young women who don't desire a child have strangely high rates of ectopic pregnancies.
* Genetic mosaicism. Has a variety of implications, ranging from brain problems (''Series/{{House}}'') to multiple sets of DNA making criminal activity tough to catch (''Series/{{CSI}}'').
** Examples of gonadal and tissue mosaicism and tetragametic chimeras (people whose bodies are the result of two embryos with different genomes fusing together at an early stage) may be more common than we think, even in humans (primarily because tests are rarely administered for it). Blaschko lines and patches on the skin or eyes of different color are a visible indicator of chimerism.
* [[SplitPersonality Multiple Personality Disorder]]: In real life this is ''so'' rare some psychiatrists doubt it actually exists at all. It's all over TV. MPD has been renamed to Dissociative Identity Disorder, but again, TV seems to forget this detail.
** Many characters with this disorder are portrayed as only have one other personality, but in fact more than half of the people of suffer from it have more than 10 and can have as many as 100 distinct personalities.
* Porphyria: A metabolic disorder that turns your skin light-sensitive and your urine deep red. Tends to turn up in the Halloween episodes of medical shows, as the former effect has led to its association with [[OurVampiresAreDifferent vampirism]]. Also somewhat infamous for being the disease that afflicted King George the Third, first and so far only British monarch to be committed to an asylum. [[note]]Probably, anyway; contemporary accounts of the symptoms are mostly consistent with it but it's difficult to say for sure.[[/note]]
* [[HollywoodTourettes Tourette's Syndrome]]: Because people swearing randomly is funny, even though less than 10% of people with Tourette's ''actually'' swear uncontrollably.
* [[UsefulNotes/AspergerSyndrome Asperger's Syndrome]]: The frequency of this disorder is uncertain (estimates from various studies range from 1 in 250 to 1 in 5,000), and diagnoses have increased in recent years, but it's likely not as common as it may appear to be on the internet. Tends to get dredged up by writers who do not realize that genius does not equate Asperger's or vice versa.
** Asperger's Syndrome can also vary in severity, from barely noticeable to outright debilitating. On TV, it's always the most severe level.
* Amnesia: ''Very'' dramatic, and lets the character start out as ignorant as the audience about what's going on. In comedies, almost any [[TapOnTheHead blow to the head]] causes, and cures, amnesia. Doesn't work ''at all'' the way it's portrayed in fiction.
** And it ALWAYS has to be retrograde amnesia.
*** [[Film/{{Memento}} Not]] [[FiftyFirstDates always.]]

Note that not every common condition on TV is an example of this; some are TruthInTelevision. If every other TV child carrying an asthma inhaler looks unrealistic, consider that the rate of childhood asthma in many developed countries is between one in ten and ''one in five''.

Related to the MillionToOneChance and ArkhamsRazor; see also YouFailYourMedicalBoardsForever. No connection to [[Film/{{Videodrome}} that TV show]] that [[BrownNote literally causes brain tumors]].


[[folder:Anime and Manga]]
* ''Manga/BlackJack'' does this, but much like with House, it makes a certain degree of sense - he's an incredibly skilled, incredibly expensive, unlicensed doctor - so he usually only gets hired by someone who've already failed to find relief from the general medical establishment, usually meaning rare and/or incurable diseases. (When Manga/BlackJack is around, you may as well tear the word 'Incurable' out of the dictionary...). There's always a point when rare becomes just plain made up. Lionitis is rare and highly unlikely; a telekinetic fetiform terratoma is just plain impossible (as far as we know).
* ''Manga/SaijouNoMeii'' features a traumatic cardiac tamponade, one of those conditions known for turning up far more in medical dramas than real life, in the very first story. Again, somewhat excusable as the series' focus is on pediatric medicine and young children are more susceptible to it than adults because their ribs aren't fully developed.

* ''Film/TheSixthSense'' included a suspicion of Münchhausen Syndrome by proxy. Possibly, either the doctor or the writer had been watching too much TV (or both since [[{{Cameo}} they were the same guy]])
* Overlapping with Theater, in ''Film/RepoTheGeneticOpera'', we have a spectacular case of Munchausen By Proxy. It's all the more over-the-top since the individual responsible [[spoiler: is a physician]] and the case has lasted for [[spoiler: seventeen years!]]

* In ''Literature/ManiacMagee'' by Jerry Spinelli, the title character is allergic to pizza. Not any of the separate ingredients in the pizza, just... pizza itself. He breaks out into a rash, with spots that look suspiciously like pepperoni.
* The page quote is discussed in Robin Cook's ''Literature/{{Outbreak}}'' when the protagonist experiences a lot of skepticism over a diagnosis of ebola. Similarly, Jack experiences skepticism over an anthrax diagnosis in {{Vector}}. There are probably lots of other examples, since Cook has written dozens of medical thrillers.

[[folder:Live Action TV]]
* The trope exists in ''Series/{{House}}'', but it's [[JustifiedTrope somewhat excusable]] there: as Dr. House specializes in diagnosing rare diseases, it's not too unreasonable to assume that the patients with more conventional diseases are being treated by more conventional doctors. It's said several times that many of the patients House treats are sent to him by other doctors who are stumped by their patient's symptoms. Also sometimes averted in House's despised clinic hours, where he must treat walk-in patients, and those patients frequently have common diseases, right down to the common cold. Periodically {{Lampshaded}} with the RunningGag, "It's never lupus."
** House actually references this in the Pilot episode.
--->'''Foreman:''' First year of medical school - if you hear hoofbeats you think horses, not zebras.
--->'''House:''' Are you in first year of medical school? No. First of all, there's nothing on the CAT scan. Second of all, if this is a horse then the kindly family doctor in Trenton makes the obvious diagnosis and it never gets near this office.
** Inverted in an episode where a patient was initially diagnosed with heat stroke, and then got progressively worse. One of the doctors, who used to specialize in third world diseases, diagnosed the patient with polio - a disease which is all but unknown in the developed world. It turns out, the doctor was poisoning the patient with thallium to mimic the symptoms of polio. To make a point. Yes. Clearly the doctor was insane; upon figuring out what he's done, House fired him and Foreman called the cops. It turns out Dr. Foreman's original diagnosis of heat stroke was actually correct. The episode ends with AnAesop from Dr. House about listening to the guy in charge (Foreman), whom he put in charge because he knows what he's doing (AnAesop about listening to authority coming from an anarchist is kind of ironic, but that's beyond the scope of this page).
** Also inverted in an episode where a kid with genetic mosaicism collapses at a basketball game. Everyone considers the possibility that it has to do with him being intersexed; turns out he was just dehydrated, and the contrast dye used for the MRI made things worse due to his impaired kidneys.
** Less justified in the increasingly common episodes where House happens upon a patient with an incredibly rare, tough-to-diagnose disorder by chance rather than because they've come to him as a last resort. In one case, the patient was someone House just happened to be on the same bus with when it crashed -- and the patient who had the rare disorder wasn't even the person whose symptoms House had noticed before the crash and spent much of the episode trying to remember.
*** That specific example justifies itself to a certain extent. House was convinced he saw an important symptom just before the crash. So, he combed through almost everyone on the bus looking for someone presenting a mysterious symptom. He happened to find one guy in the group of dozens of people who actually did have an undiagnosed condition with a small symptom (which would have developed eventually, but was not immediately life-threatening in the meantime, especially compared to the bus crash).
** One time, actually [[spoiler:it ''was'' lupus.]] [[FanonDiscontinuity But nobody ever seems to remember it.]]
** Averted in the [[TearJerker most horrible way possible]] when Foreman misdiagnoses a woman, when she had a simple staph infection. Foreman's misdiagnosis killed her.
** Was also averted in one episode. House and Cuddy were on an airplane returning from a conference about rare infectious diseases. When a passenger got sick, Cuddy thought it was one of those diseases, and it seemed she might be right when another passenger displayed similar symptoms. Despite the symptoms, the passengers had entirely different things wrong with them. [[spoiler: The first had been scuba diving and surfaced too quickly, the other was pregnant. The rest of the people puking were just suffering from a plain mass hysteria.]]
* ''Series/{{Scrubs}}'':
** Inverted. JD diagnoses a patient with Kuru, which is confined to Papua New Guinea and transmitted by cannibalism. He's mocked mercilessly by his attending and the patient himself, and the disease turns out to be mundane. Dr. Cox actually fully describes this trope in his rant, saying that the patient is probably just experiencing ordinary disease with unordinary symptoms. He's right. Even so, most patients on the show have something fairly obscure, if not actually rare.
** Averted, where a news broadcast goes out about two Hepatitis A cases. The hospital is then crushed with people thinking they have it.
--->'''Dr. Cox''': And you know what happens next? Every hypochondriac with the sniffles is gonna come thundering through those doors. So enjoy the next few days of peace and quiet.
** Another episode has J.D. suspect a patient has [=SARS=]. He doesn't and everyone gets angry at him for suggesting this, because the hospital gets quarantined so no one can leave.
* ''Series/GreysAnatomy''. This could take a while...
** Tumor causing penis to stay erect (priapism)
** Girl who can't stop experiencing spontaneous orgasms
*** This is persistent sexual arousal syndrome, a real condition that they both underplay (the woman in the show experiences under ten a day, where real-world cases have the woman experiencing hundreds) and demean her with all of the usual "lucky sod" reactions. Yes, because spontaneously having orgasms against your will when you may even be actively fighting against it in a manner that will likely make it impossible to form or maintain a romantic relationship is just what the doctor ordered.
**** While that is the doctors' first reaction, the patient suffering from the disease gives a [[{{CrowningMomentof Awesome}} speech]] to the doctors that explains just how debilitating the disease is in her life.
** Man's penis piercing getting caught on the inside of his ex-wife's IUD during sex.
** Lionitis
** Vaginal poison oak rash
*** Embarrassing, but it happens. Be careful what you wipe with!
** Removal of a semi-digested book from a depressed author's stomach.
** Separation of adult siamese twins (played by the [[Series/CheapSeats Sklar brothers]]) who are joined at the spine and both in love with the same woman. The episode actually went to great pains to point out how completely impossible the procedure was. [[MillionToOneChance Then they succeeded in doing it.]]
** Girl with a misshapen spine at a 90-degree angle. She had VATER (now known as VACTERL) syndrome either combined with scoliosis or completely separately.
** Man shot in the chest at point blank range with a bazooka.
** Discovery that a little girl actually has XY chromosomes but is resistant to testosterone.
*** This would be [[http://en.wikipedia.org/wiki/Androgen_insensitivity androgen insensitivity syndrome]]. Not that the average sufferer would really have enough medical problems that they would end up in the clinic except from unrelated issues.
** Woman with radiation poisoning emitting toxic gas from her stomach while being operated on.
** Necrotizing fasciitis: Flesh. Eating. Bacteria. This has also shown up on ''Scrubs'' at least three times.
*** This is rare, but not incredibly terribly so; it's a risk that has to be guarded against whenever you cut someone open. Most famously, the Prime Minister of UsefulNotes/TheNetherlands in 2004, Jan Peter Balkenende, had to be hospitalized for several weeks after catching the disease and being treated for it.
** Woman born with two uteruses, pregnant with the children of two different men at the same time.
*** This one has also happened in real life; Google "uterus didelphys" if you like. The most recently reported case was in 2009, in a woman with two uteri and two vaginas.
*** Twins with two different fathers aren't all that rare either, although they're usually roommates in a single uterus.
** Quintuplets.
** Giant pylon falling on a woman's face, making her bruised beyond recognition, and also amnesiac. ''While pregnant.''
** ''Fish. Lodged. In. Penis.'' (And if you think that this one is too absurd to be real, [[http://en.wikipedia.org/wiki/Candiru think again.]]. Incredible painful and disfiguring, but also vanishingly rare even in those places where candiru actually are found. There is one [[http://www.google.com/translate?u=http%3A%2F%2Fweb.archive.org%2Fweb%2F20040616043555%2Fhttp%3A%2F%2Fwww.internext.com.br%2Furologia%2FCasosclinicos.htm&langpair=pt%7Cen&hl=en&ie=UTF8 documented case]])
** Clairvoyance and a brain tumor.
** A nineteen-year-old boy encased in cement.
** 100% face transplant. Better still, the guy was able to take the bandages off within the day, and had almost no negative physical effects whatsoever.
** Super-fat man dying of super-fatness.
** Woman near-drowned, and with hypothermia, being legally dead for a few hours, then surviving. This one [[TruthInTelevision actually happens]], though - [=EMTs=] are even trained on care for near-drowning hypothermic patients. But in this case, she suffers no lasting effects. [[spoiler:This was a case of ContractualImmortality -- it was the eponymous character!]]
** This was played with in the flashbacks during an episode of LOST featuring Mr. Eko as well.
** Guy hit by a bus after pushing a girl out of its way, gains a bruised-beyond-recognition face and loss of motor skills [[spoiler:which make the docs unable to tell that it's George]].
** A woman with a skin cancer that's spread to her brain and caused her hallucinations of a dead love [[spoiler:and happens to be Izzy. My, the main characters certainly provide their friends with a lot of practice...]]
** A pine tree growing in a man's lung.
* Inverted once on ''DoogieHowserMD''. A celebrity came in to the hospital after a trip through third-world countries with an illness none of the doctors recognized immediately. They did tests for all sorts of unusual diseases, until a nurse recognized it as measles, which wasn't recognized solely because immunizations for the disease are nigh-ubiquitous.
** TruthInTelevision. Most doctors graduating in the past few decades have never seen an actual live case of measles. Though in the US at least, [[TooDumbToLive "anti-vaxxers"]] [[http://io9.com/what-happens-when-you-dont-vaccinate-1631423511 are slowly changing this.]]
* Manages to make its way into ''Series/{{Mash}}'' occasionally, even though they are in a war zone. Its mostly {{averted|Trope}}, though. The most "uncommon" diseases that rolled through the 4077th were hemorrhagic fever and malaria, and in the malaria episode Klinger and another corpsman both had a reaction to the anti-malarial medication being issued. Such a reaction is TruthInTelevision and was unknown at the time (people of African descent were known to have a reaction to the medication, but people of Arab descent like Klinger were ''not'', until it started showing up).
* Played realistically on ''GoldenGirls''. Dorothy was struck with a strange illness that left her perpetually lethargic. She had gone to several doctors and traveled to a specialist in New York, only to be told she was just getting old and should do something new like get her hair done or some nonsense. It was only after a 5th (?) opinion that she was diagnosed with the rare Chronic Fatigue Syndrome. This episode was inspired by one of the produces coming down with this same disorder.
** Actually, CFS is a diagnosis of exclusion (that is, when every known cause of fatigue has been ruled out you call it CFS), and there is no specific treatment. Getting diagnosed with CFS isn't really all that helpful. If Dorothy was the kind of person who enjoyed getting a new hairdo, that actually wouldn't be a bad idea to help relieve her symptoms.
* One episode of ''Series/LieToMe'' had a suspect with Dissociative Identity Disorder, correctly named and handled with slightly more accuracy than most places. For someone it was called "the holy grail of psychology".
* Partially deconstructed as part of a BStory in the short-lived FOX series ''Mental''. The father of one of the doctors [[ImNotADoctorButIPlayOneOnTV plays a doctor on television]] and, mimicking his acting job, diagnoses a patient with [[http://en.wikipedia.org/wiki/Mad_hatter_disease Mad hatter disease]] and orders a blood test on her. The real doctor is annoyed at his father practicing medicine without a license... until a nurse comes in and asks how he made the connection, as the disease is really rare.
* Parodied in ''BoyMeetsWorld''. Turns out Cory's just a hypochondriac.
* On channels like TLC and Discovery Health, they will often show specials about people with these diseases to dispel the myths about it (like the special on Tourette's where none of the children with it actually swore).

* As stated under Film, in ''Film/RepoTheGeneticOpera'', we have a spectacular case of Munchausen By Proxy. It's all the more over-the-top since the individual responsible [[spoiler: is a physician]] and the case has lasted for [[spoiler: seventeen years!]]

[[folder:Stand Up Comedy]]
* Creator/JeffFoxworthy hangs a lampshade on it, retelling his wife's over-reaction every time she sees an article about a disease on 60 Minutes.
-->'''Jeff's Wife:''' I got it... I have every one of those symptoms!
-->'''Jeff:''' You do ''not'' have testicular cancer! You don't even have testiculars!

[[folder:Web Comics]]
* ''TheDragonDoctors'' were formed specifically to treat rare diseases-- ''magical'' diseases. The author has been quoted as saying that since quite a lot of medical dramas just plain make up their ailments, he might as well not bother setting it in the real world. The solutions are always presented in a logical fashion, however.

* ''WesternAnimation/TheSimpsons'':
** In 'The Mansion Family," Mr. Burns was diagnosed with '''every''' disease.
-->'''Doctor''': Mr. Burns, I'm afraid you are the sickest man in the United States. You have everything.\\
'''Mr. Burns''': You mean I have pneumonia?\\
'''Doctor''': Yes.\\
'''Mr. Burns''': Juvenile diabetes?\\
'''Doctor''': Yes.\\
'''Mr. Burns''': Hysterical pregnancy?\\
'''Doctor''': Uh, a little bit, yes. You also have several diseases that have just been discovered - in you.
** In "Blood Feud," Bart's allergies include both butterscotch and imitation butterscotch.