Elayne Heilveil had a role in the film as one of the patients, but due to re shoots and ongoing production problems, her scenes were cut from the final film, but she appeared in promotional material.
Sharon Farrell claimed that the poster of her on the cover, with the title of the movie, The Fifth Floor, was on the wall on the fifth floor of the Playboy Building.
Although Sharon Farrell is not the main character (Dianne Hull is), her image alone adorns on what's the main poster image of the film, making her seem to be the main character.
One of the mental patients is played by Cathey Paine, who played Manson Family killer Leslie Van Houten in Helter Skelter, and she wields a knife in Avalanche, which came out the same year as this film.
Michael Berryman was in One Flew Over The Cuckoo's Nest, the blockbuster also set in an insane asylum.