From The Grindhouse Cinema Database
- William Lustig and Joe Spinell, say they didn't always have the necessary permits to film on location in New York City. Certain scenes (including the infamous shotgun through the windshield scene) had to have been filmed quickly and afterwards the crew had to run away before the cops arrived.
- Daria Nicolodi was originally cast to play Anna D'Antoni, but she was unable to go to New York for filming because she was still filming her scenes for the movie Inferno (1980) in Italy.
- The opening scene on the beach was inspired by the opening scene from Jaws (1975) from the point-of-view of the stalking shark.
- The headless corpse in the end is the Betsy Palmer corpse (Jason's mother) from Friday the 13th (1980). The helicopter shots are recycled footage from Inferno (1980).
- The scenes in Frank Zito's tiny apartment were inspired by the Swedish thriller Mannen på taket (1976) ("The Man on the Roof") with the claustrophobic setting and the quiet tone with a dripping faucet and occasional sound of traffic. The color and crude décor of the apartment and other sets were inspired from the color-theme sets of Italian horror thrillers such as Profondo rosso (1975) ("Deep Red"), Suspiria (1977), Sei donne per l'assassino (1964) and several others.
- Because they would only have one chance to film the scene where Tom Savini's character gets shot, Savini decided that he should be the one to pull the trigger. He said it felt a little weird shooting the dummy he had created of himself in the face.
- A 1979 post-production ad for Variety magazine stated some of the cast as including Daria Nicolodi, Susan Tyrrell and Jason Miller opposite Joe Spinell. Nicolodi was offered the lead role but was unavailable, and no information has yet surfaced to reveal which roles were to be played by Tyrrell and Miller.
- The film originally had a title song of the same name, but in the end was not used. The lyrics were toned down and the song, "Maniac", was used in Flashdance (1983).
- In order to keep costs down, several porn actresses, such as Gail Lawrence, were hired to play the victims and other minor female roles.
- Joe Spinell's salary for Maniac (1980) $0. (10-15% of proffits)
- The film is banned in Germany.