Actor-Inspired Element: The script called for Dr Loomis to look shocked when Michael Myers's body disappears from the lawn. Donald Pleasance argued that he should have an "I knew this would happen" look. They shot it both ways and the latter was the one used.
California Doubling: The movie was filmed in California, as opposed to Illinois. In several documentaries, Jamie Lee Curtis and John Carpenter point out the various palm trees that can be spotted in the background.
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.
Creator Cameo: Both Tommy Lee Wallace and Debra Hill appear in Michael Myers's costume. Additionally John Carpenter provides the voice of Annie's boyfriend Paul on the phone.
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.
Recut: During the filming of the sequel, John Carpenter shot more scenes for the ABC broadcast of the film to help it pad out the allotted time. While largely just character exposition, one scene (a visit to Michael's asylum room where the word "sister" is carved in the door) serves to help validate the twist of the second movie.
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.
The original script had the story take place over several days. Due to budget reasons (reducing the number of costume and location changes), it was reduced to one day and Halloween was the most appropriate night for it to happen.
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.
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.
Working Title: The initial storydraft was called The Babysitter Murders.