In the book, Mary lives and works in Ft. Worth, Texas; in the movie, Marion lives and works in Phoenix, Arizona. In the book, Mary is a brunette; in the movie, Marion is a blonde. In the book, there is no tryst between Sam and Mary at a hotel, as in the movie. In fact, they are not even lovers, although they are engaged. In the book, Mary does not pull off the road and sleep overnight in her car, as Marion does in the movie; so no cop questions, and then follows, her. In the book, Mary trades cars twice, not once as Marion does. The book begins at the Bates Motel, with the first portion of the novel focusing on Norman's unhappy domestic life with "Mother." He is a shy, morbidly obese man in his mid-forties, who wears glasses. In the movie, Norman is thin, much younger, and does not wear glasses.
In the book, when Mary arrives at the motel, Norman treats her in a gruff, sometimes hostile manner. In the movie, Norman is friendlier and more relaxed around Marion. In the book, Mary signs the motel register "Jane Wilson"; in the movie, Marion's alias is "Marie Samuels". In the book, Mary goes to the house to have supper with Norman, and they eat in his kitchen. In the movie, Norman brings the food to the motel on a tray, and they eat in the parlor adjoining the office. In the book, there is only one stuffed squirrel on display. In the movie, there are several stuffed birds. In the book, there are six cabins; in the movie, there are twelve. In the book, Norman's peephole is obscured by a framed hotelier's license; in the movie, it is covered by a painting. In the book, Mary leaves the money in the glove compartment of her car. In the movie, she wraps it in a newspaper.
When "Mother" attacks Mary in the shower, she kills her by severing her head rather than just stabbing her. Afterward, Norman wraps the body in an oilcloth he retrieves from the house, not in the shower curtain. When the Lila Crane of the book first meets Sam Loomis at the hardware store, it is night and the store is already closed. In the dim light, Lila looks so much like Mary, that he takes her in his arms and kisses her, an action she angrily rebuffs. In the movie, Lila arrives at the store during the day and no such mistake is made.
In the book, it is revealed that Norman's blackouts--meaning the times when he switches over to the mother personality --are the direct result of his getting drunk and that so long as he remains sober he is able to keep his homicidal impulses under control. In the film, Norman never drinks. When Sam and Lila go to the motel, they know which cabin Mary was in because the cabin number is written in the register. So they request that cabin, and in it they find an earring belonging to Mary. In the movie, the private detective, Arbogast, discovered which cabin she had stayed in during his interview with Bates, and he mentions it to Lila over the phone. In the bathroom, they find a piece of paper with figuring on it that Marion had tried to flush down the toilet. After Sam and Lila find Mary's earring, Lila is determined to talk to "Mother". Sam is against the idea, so she tells him that she is going to drive into town and gets the Sheriff. Sam engages Norman in conversation while she drives away. But she stops up the road, and turns the car around, which is seen by Norman but not Sam. She then goes into the house alone. In the movie, Sam agrees to let her go into the house by herself, and he keeps Norman occupied while she does so.
In the book, "Mother" and Joe are poisoned while eating a celebratory dinner. In the movie, they are found dead in bed, and it is implied that they were being intimate at the time. The deaths occurred twenty years before the story begins; in the movie, they happened ten years earlier. In the book, Norman is committed to a sanitarium immediately following the discovery of the bodies. When he is released four months later, he digs up his mother's coffin and recovers the corpse. In the movie, he removes the body from the coffin prior to the burial, and replaces it with something of equal weight.