Actor-Inspired Element: The script called for Dr Loomis to look shocked when Michael Myers's body disappears from the lawn. Donald Pleasence argued that he should have an "I knew this would happen" look. They shot it both ways and the latter was the one used.
Completely Different Title: In Sweden, the film became All Saints' Bloody Night. In Italy, it was called Witch's Night, since Halloween was not commonly celebrated there at the time.
Creator Backlash: Both John Carpenter and Debra Hill expressed displeasure at the Death by Sex trope's rise in horror after this movie. They said the reason the horny teenagers got killed was because they were too busy trying to do it that they failed to notice a killer approaching. Laurie only survives because she's on her own for most of the film.
Credits Gag: The score is apparently performed by "The Bowling Green Symphony Orchestra" — at a time when there was no orchestra of that name.
Dawson Casting: All of the teenagers are played by actors in their late twenties/early thirties. Even the least severe example—17/18-year old Laurie played by then-20 year old Jamie Lee Curtis.
Missing Trailer Scene: An alternate version of Lynda on the phone to Laurie was shot for the trailer, because PJ Soles's blouse was open in the final film. So in the trailers and publicity stills, she is wearing a bathrobe instead.
No Budget: Only $320,000 was spent for this film, which is pretty amazing considering that it made $35,000,000.
Novelization: A very rare one now, that revealed a few plot points about Michael. It answers the Plot Hole about how Myers knows how to drive - by watching Loomis carefully operate the car during their many sessions apparently. It also heavily suggests that Michael is possessed by the ghost of an ancient Celtic boy who murdered a girl he was in love with, making Michael an innocent victim.
Real Life Writes the Plot: The original script had the murders take place over several days. Due to the low budget, filmmakers minimized the amount of set and costume changes and had the story happen only on one night. This also wrote the title, as they decided to place the plot on Halloween night.
Re Cut: The 1981 NBC broadcast featured a new cut of the movie with less violence, and 12 minutes of additional scenes shot during production of first sequel with mostly the same crew, and Pleasence, Curtis, Soles, and Kyes reprising their roles. They were all toward the beginning of the film, and mostly just exist to pad out the runtime, and to tie the story more directly into the sequel. This cut was used for almost all TV broadcasts until the late 90s, when the film was first remastered. Around that time, an "extended cut" was also released to VHS and DVD that was basically the original theatrical cut with the additional scenes included. These scenes were also included as a separate bonus feature on the 2013 Blu-ray, but, due to fan demand, the full "extended cut" was included in the deluxe boxset in HD as a bonus feature (with the added scenes in SD). Fan reaction to these scenes is mixed. They're generally accepted as canon, but some (including Carpenter himself) think they hurt the movie's pace, and establish too much backstory. There are also fans that can't watch this movie without them. Since they set up the future sequels, they work better when this film is viewed more as the first entry in the franchise instead of a standalone feature.
Romance on the Set: Nancy Loomis dated and eventually married Tommy Lee Wallace. They ended up divorced.
Dennis Quaid was offered the role of Bob (Lynda's boyfriend) since he was dating P.J. Soles at the time, but had to turn it down due to work on another movie.
There were two masks to choose from - the more familiar Captain Kirk mask, and a Monster Clown one (as a nod to Michael killing his sister while dressed as a clown). While they found the clown one scary too, the Captain Kirk one was ruled better because it was emotionless. Other masks considered include Richard Nixon, Spock and Emmett Kelly.
Originally, Dr. Loomis was supposed to have a phone conversation with his wife. Donald Pleasence didn't do it, saying he thought the character shouldn't have a family or a past.
There was originally no music in the film at all. When one female critic complained the film wasn't scary, John Carpenter composed a score in three days.
Anne Lockhart, daughter of Lassie's June Lockhart, was Carpenter's first choice for Laurie. But she had other commitments and couldn't do it.
Working Title: The initial storydraft was called The Babysitter Murders.