Continuity mistake: After Norman argues with Mr Toomey, before he goes up to the house, you can plainly see the light on in the living room where Mary is sitting. When Norman goes in the house, Mary is sitting in the dark and Norman then turns on the light.
Continuity mistake: When Norman is painting the motel, he is distracted by someone looking out the curtains of his house and he drops the paintbrush straight. But in the next shot the paint brush has moved at a forty-five degree angle to how it landed. (00:43:55)
Continuity mistake: When the two teenagers are down in Norman's fruit cellar, and a "lady" with a knife is chasing the boy, he leaves finger markings on the fogged up window. But by the next shot they have changed. You can tell because when the boy made the markings, his thumb and his index finger markings intersected, but when the camera angle changes the finger prints don't intersect and they are noticeably straightened also. (00:49:45)
Continuity mistake: Near the end where a lady is coming up the stairs to the Bates house, her hair is tied up much like the "Mother" wig, but when the lady arrives, who turns out to be Mrs. Spool, her hair is parted very differently. (01:40:40 - 01:41:10)
Continuity mistake: When Norman arrives home, he is startled by a note that is found beside the phone and he accidentally knocks his suitcase down the stairs and most of his clothes land on the top of the stairs. But as the camera angle switches to the bottom of the stairs, the clothes are further down the staircase. They couldn't have moved as they were stationary at the end of the other shot. (00:10:15)