Trivia: In the opening scene in New York Public Library, the librarian walks down the reading room with her trolley full of books and a man appears and walks across the screen. This man is the film's associate producer, Joe Medjuck.
Trivia: 1980s pop star Debbie Gibson has a cameo as the girl with the pink bow in her hair, celebrating her birthday at the Tavern on the Green.
Trivia: When Spengler, Venkman and Stantz are in the basement of the New York Public Library, the bookcase falls over, prompting Venkman to ask Stantz if this has ever happened before. The whole exchange, including the bookcase falling over, was not scripted. It is thought that the bookcase fell because some crewmen accidentally bumped into it, and Bill Murray ad-libbed his lines. Producer/director Ivan Reitman decided to leave it in the movie because it added to the supernatural qualities of the film.
Trivia: The original script by Dan Aykroyd took place in the future, and revolved around just one of many different "Ghost Smasher" teams operating throughout the galaxy. (As the original title was "Ghost Smashers.") The "Stay-Puft" Marshmallow-Man appeared by the 30-minute mark of the script and was just one of numerous giant threats the team would face. The budget was projected at nearly $300 million (in 1984 dollars, unadjusted for inflation), so Harold Ramis was brought in to help rewrite the script to make it more manageable for studios. (Hence, it was relocated to modern times, and the large set-pieces were scaled back).
Trivia: After the containment unit explodes, adult film star Ron Jeremy can be seen among the crowd witnessing the chaos, on the left side of the screen behind a blue police barrier.
Trivia: The Ghostbusters theme, "composed" by Ray Parker Jr., was directly ripped off from the song "I Want A New Drug" by Huey Lewis and the News. In fact, Huey Lewis sued Ray Parker for intellectual property theft (settled out of court). Premiere Magazine later featured an article in which the film makers admitted to using the song "I Want a New Drug" as temporary background music in many scenes. They said that they made an offer to Huey Lewis to write the main theme for the movie, but Huey Lewis declined. The filmmakers then provided Ray Parker Jr. with finished film footage (including the Huey Lewis song in the background) to aid Ray Parker in writing an original theme song, which apparently he couldn't do.