When filming the first murder scene, Henry Thomas got so involved in the stabbing that part of the knife went into his hand which caused some nerve damage. To this day, he still has a scar.
Anthony Perkins and Psycho III (1986) screenwriter Charles Edward Pogue originally pitched an idea for Psycho IV that had Norman's house and motel getting turned into a tourist attraction for horror weekends. Norman then escapes from the mental institution with a mute patient. The actor who was set to play Norman Bates for the horror weekend quits and when Norman comes home he gets hired to play himself. Pogue claims that it was meant to be a black comedy but Universal opposed the idea.
When Anthony Perkins saw the first screening of the film, he called it the best out of all the Psycho sequels.
Contrary to popular belief, only one ending was shot for the film. Director Mick Garris has stated in interviews that Janet Leigh saying in her introduction for the broadcast on Showtime that multiple endings were shot was just a publicity stunt by Universal.