The original title of Ghostbusters was Ghost Smashers.

The "marshmallow" at the end of the movie is shaving cream.

Two points in the movie where you can see Staypuft Marshmallows: the first is next to the eggs on Dana's worktop when the eggs start to cook, and the second is when the beam of light is coming out of the Ghostbuster's house, there is a wide shot of it and on the left of the screen there is a billboard advertising Staypuft Marshmallows.

Writer Dan Aykroyd originally wrote the role of Venkman for John Belushi, but approached Murray after Belushi's death. Belushi still appears in the movie (of sorts): the body movement of the Slimer Ghost were based on his movements.

The Ghostbusters Fire House is located at North Moore, & Varick St. in New York, NY.

Casey Kasem does a voice-over cameo as himself on his radio show after the Ghostbusters become famous. The ditsy blonde woman that Louis dances with at his party is played by Casey's wife, Jean Kasem.

The role of Louis Tully was originally written and storyboarded for John Candy.

Venkman mentions the time Egon "tried to drill a hole in his head". This is a reference to Trepanation, a procedure alleged to increase psychic abilities among other things.

Originally, Gozer was supposed to be a man and the top choices for the character were David Bowie (the decision to get him was made too late to hire a famous actor) and Paul Ruebens (and he was supposed to appear in a business suit).

Scene where Venkman gives Egon the candy bar and says, "You've earned it": in the original film version, Venkman gives Egon a Nestlé Crunch bar; in the VHS/DVD versions, the candy bar is a Payday. I'm guessing there was a contract dispute with Nestlé sometime between the film release and the video release of the movie.