- Actor-Inspired Element: Olivia Hussey didn't want to just play Norma as 'crazy', so she took inspiration from the actor Christopher Jones (of Ryan's Daughter fame) - with whom she'd been in an abusive relationship. She saw Norma as someone who deep down knew she was wrong but had lost control of her mind.
- California Doubling: Filmed in Orlando, Florida instead of Hollywood like the previous three films, even though the film is still set in Southern California.
- Hostility on the Set: Mick Garris later called Anthony Perkins the most difficult actor he ever worked with.
- Jossed: Janet Leigh announced on Showtime that multiple endings were shot for the film. Mick Garris later set the record straight, saying that only one ending was shot and it was just a publicity stunt by Universal.
- Method Acting: When filming the first murder scene, Henry Thomas (Teenage Norman) 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.
- The Other Darrin: Virginia Gregg usually provided the voice of Norma Bates. As she had passed away four years previously - and Norma physically appears for the first time - Olivia Hussey played the role now.
- Playing Against Type: Olivia Hussey - who had played characters like Juliet, the Virgin Mary and Rebecca (and even in horror films like Black Christmas (1974) and Turkey Shoot was still a Final Girl) - as the abusive Norma Bates.
- Recycled Set: Averted, as for this film brand new sets were constructed for both the Bates Motel and the Bates Mansion at Universal Studios Florida, rather than just reusing the original sets at Universal Studios Hollywood (which had been heavily modified for Bates Motel (1987)). After filming wrapped, the sets continued to stand for several years; at one point being used for a Psycho-themed haunted house attraction at Halloween Horror Nights. The sets were finally bulldozed towards the end of the '90s, in order to make room for the Woody Woodpecker's KidZone area.
- Throw It In!: The scene where Norman rips the apple in half was improvised by Anthony Perkins. In the script, Norman was originally supposed to take a butcher knife and slam it into the apple but Perkins felt that was too corny.
- What Could Have Been:
- Back when the film was planned as a theatrical picture, Anthony Perkins and Psycho III screenwriter Charles Edward Pogue had a pitch for a dark comedy sequel where Norman's house and motel were turned into a a haunted house tourist attraction. Norman, having escaped the institution, ends up hired to play himself when the actor originally hired for the attraction quits.
- Rumors floated around after the film's release of a fifth sequel which would have involved Norman's son. A combination of Omen IV: The Awakening being released the following year and using a near-identical plot (albeit with Damien Thorne's daughter rather than a son), along with Anthony Perkins dying of AIDS the year after that, put an end to any such plans.
- There were talks about having the flashbacks to Norman's childhood in black and white, to match the first film.
Trivia / Psycho IV: The Beginning