Director Lamberto Bava said in an interview that he liked the American title for the film (A Blade in the Dark) much better than the Italian title (House of Dark Stairs). Bava felt that particular title captured the film much better.
Originally filmed as a four-part, half-hour, suspense mini-series for Italian TV with one killing at the end of each part. It was then turned into a theatrical movie when TV networks rejected it for being too violent to air on network television.
The trivia item below may give away important plot points.
For the role of the killer, Bava had a difficult time finding a man that could convincingly appear to be a woman when dressed as one. After many auditions he turned to his assistant, Michele Soavi, and cast him in the role.