History Main / RevolvingDoorCasting

** ''Just Add Water'' didn't fall victim too extremely; while numerous supporting characters vanished rather inexplicably when Season 2 began, the main cast -- consisting of mermaids Emma, Rikki, and Cleo and Cleo's boyfriend Lewis -- lasted through Seasons 1 and 2. Emma's actress was unable to return for Season 3 and was replaced with new mermaid Bella, while Bella's love interest Will was also made a main cast member right away (effectively replacing Emma's second love interest Ash, the only Season 2 supporting character to be noticeably absent from Season 3, as his continued presence wouldn't make much sense without Emma). Lewis had to depart halfway through Season 3 but came BackForTheFinale.
** ''Mako Mermaids'', however, had to replace mermaids far more often, with the entire original trio being PutOnABus over the course of the series resulting in a completely different trio at the end. Zac, Evie, and the entire supporting cast lasted all three seasons.
*** Season 1: Lyla, Nixie, and Sirena, featuring Zac
*** Season 2: Lyla and Nixie are replaced by Mimmi and Ondina; Evie is PromotedToOpeningTitles and Erik debuts [[spoiler:but has a FaceHeelTurn at the end of the season and does not return for the third]]
*** Season 3: Sirena is replaced by Weilan

** ''Just Add Water'' didn't fall victim too extremely; while numerous supporting characters vanished rather inexplicably at the end of Season 1, the main cast -- consisting of mermaids Emma, Rikki, and Cleo and Cleo's boyfriend Lewis -- lasted through Seasons 1 and 2. Emma's actress was unable to return for Season 3 and was replaced with new mermaid Bella, while Bella's love interest Will was also made a main cast member right away (effectively replacing Emma's second love interest Ash, the only major Season 2 character not to return as his continued presence wouldn't make much sense without her). Lewis had to depart halfway through Season 3 but came BackForTheFinale.
** ''Mako Mermaids'', however, had to replace mermaids far more often, with the entire original trio being PutOnABus over the course of the series resulting in a completely different trio at the end. The non-mermaid leads and most other supporting cast remained consistent.

** ''Just Add Water'' didn't fall victim too extremely; while numerous supporting characters vanished at the end of Season 1, the main cast -- consisting of mermaids Emma, Rikki, and Cleo and Cleo's boyfriend Lewis -- lasted through Seasons 1 and 2. Emma's actress was unable to return for Season 3 and was replaced with new mermaid Bella, while Bella's love interest Will was also made a main cast member right away. Lewis had to depart halfway through Season 3 but came BackForTheFinale.

*** Season 1: Lyla, Nixie, and Sirena
*** Season 2: Lyla and Nixie are replaced by Mimmi and Ondina

* The original version of ''Series/{{Survivors}}'' was only on the air for three seasons, and only actress Lucy Fleming lasted through the entire run. This came about partly due to behind-the-scenes [[TroubledProduction turmoil]], and the series being a post-apocalyptic AnyoneCanDie scenario.

* For a series that had five full seasons and two truncated ones, and focused heavily on the personal lives of the characters, ''Series/HomicideLifeOnTheStreet'' actually had a surprising number of cast changes; so many that Richard Belzer, Clark Johnson, Yaphet Kotto and Kyle Secor were the only four cast members (out of 19) to last from start to finish.

*** The revival series, which launched in 2005, has kept to this format, with several companions leaving after only one season (though they came back for guest appearances later), a couple staying for two seasons, and only three modern-era companions (Amy, Rory, and Clara) staying for more than two complete seasons.

* ''Series/LawAndOrder'' and its assorted spinoffs. When Diane Neal left SVU, she actually said she was surprised she lasted as long as she did, considering Creator/DickWolf is known for liking to constantly rotate its cast members. The original series ran for twenty years before its reboot, and the last original cast member, Steven Hill, left after ten. If you don't count him as original because he wasn't in the pilot, the last one left after five (Creator/ChrisNoth).

* The process is slower than in other examples, but ''Series/{{Degrassi}}'' has gradually retired its early characters in favor of new ones. Snake is the only one who's been a main character the whole time, and he's usually a minor character.

* Unlike other Series/{{Arrowverse}} series, which have a core cast of characters, ''Series/LegendsOfTomorrow'' swaps heroes in and out on a regular basis -- characters often disappear for a season before returning as regulars. Guest appearances of former main cast members tend to be the rule, rather than the exception. Main characters are added and removed at any time during the season, suggesting that the series showcases DC characters by design. As of mid-Season 7, the only actors that have been on the show from the start are Creator/CaityLotz (Sara Lance/White Canary) and Creator/AmyPemberton (Gideon, the Waverider's sentient AI), the latter of whom mostly does voice acting.

** As of Season 20, the only cast members still remaining in the main cast from Season 1 are [=David McCallum=] as Ducky, Sean Murray as [=McGee=], and Brian Dietzen as Palmer--the latter two having not been listed as main cast in season 1 (in Dietzen's case, rightly so as he was more of a recurring character), and [=McCallum=] are [[AdvertisedExtra not actually being a regular anymore]], with Ducky becoming a recurring character starting season 15 and his screentime is noticeably dramatically reduced especially in the recent episodes, with [=McCallum] only appeared three episodes in the eighteenth season at one point and Gibbs (portrayed by Creator/MarkHarmon) leaving the show just 4 episodes into the nineteenth season (and being more of a guest star for those four episodes; Harmon wanted to leave the show at the end of Season 18, but the network said they wouldn't renew the show without him on it).

** As of Season 19, the only cast members still remaining in the main cast from Season 1 are Mark Harmon as Gibbs, [=David McCallum=] as Ducky, Sean Murray as [=McGee=], and Brian Dietzen as Palmer--the latter two having not been listed as main cast in season 1 (in Dietzen's case, rightly so as he was more of a recurring character), and the former two [[AdvertisedExtra not actually being regulars anymore]], with Ducky becoming a recurring character nearly half a decade earlier and Gibbs leaving the show just 4 episodes into the season (and being more of a guest star for those four episodes; Harmon wanted to leave the show at the end of Season 18, but the network said they wouldn't renew the show without him on it).

* ''Series/BabylonFive'' had a bit of this, due to castmembers being written out for various reasons and replaced with new characters to take up their positions, starting with [[TheCaptain station commander]] Jeffrey Sinclair being replaced in the second season by John Sheridan due to actor Michael O'Hare's health problems. The penultimate episode of the series has Sheridan, Delenn, and Lennier leaving, and taking one last look at the station, seeing the station's new leadership watching them from Command and Control. The shot is similar to a cast shot from the first season's intro, but the only original cast member left on the station is Vir, once an assistant and now an Ambassador (and he wasn't even in the original pilot).

* ''DreamTeam'', the British soap opera set in a soccer club, featured dozens of characters during its ten-year run, the great majority lasting a year or so. And an ''absurdly'' high death toll for a soccer club.

A show which suffers an excessive regular turnover in the main cast. Regulars might last for a season or two at the most and even the (seemingly) most vital characters have a very high chance of being dropped at the end of the year. This is not merely a large cast- the core cast at any one time might be pretty small, just prone to being replaced.

Generally, this happens most organically where a series is mostly concerned with a place of work such as a [[Series/{{ER}} hospital]] or [[Series/TheBill police station]] at which some turnover might be expected, but it is not limited to such. For obvious reasons this is much more likely to happen in a {{Long Runner|s}}; Long-running shows without turnover frequent enough to qualify for this designation might still qualify for LongRunnerCastTurnover.

** The Dark Continent Arc: Too early to tell, thanks to a SeriesHiatus and the large number of characters involved so far.

* ''Series/{{Angel}}'':
** Season 1: The initial main cast is Angel, Cordelia, and Doyle. Doyle dies midseason and is replaced by Wesley.
** Season 2: Gunn joins the main cast.
** Season 3: Fred joins the main cast.
** Season 4: Connor joins the main cast. Lorne joins midseason.
** Season 5: Cordelia dies and Connor leaves the main cast, replaced by Spike. Harmony joins midseason. The final main cast is Angel, Wesley, Gunn, Fred, Lorne, Spike, and Harmony. At the end of the show, two of the original three characters [[spoiler:have died]], and at least one new character was accumulated every season.