Sir Alfred Hitchcock cast Barry Foster and Billie Whitelaw in Frenzy (1972) after watching their performances in this movie.
Much of the interior house footage was shot on location at the Mills family home in Twickenham.
This movie's controversial nature led to a prologue being added during post-production, explaining that there was no connection between "Mongolism" (Downs Syndrome) and psychopathic behavior.
The whistling theme from the score was resurrected in Quentin Tarantino's Kill Bill: Vol. 1 (2003). Elle Driver (Daryl Hannah) is whistling it as she enters the hospital. As well as this, it was also used in various episodes of American Horror Story (2011) season one.
According to a Bernard Herrmann soundtrack album, the whistler's name is Gareth Williams. Williams is also credited with some work on the orchestration of the piece.