Factual error: After Robert De Niro awakens, Robin Williams takes him on a ride around New York and Robert is amazed by all the surroundings. The movie is set in the early 1970s, but you can see plenty of vehicles around from the time that the movie was filmed (1990). Notice the square headlights that originally appeared in the late 70's.
Continuity mistake: When Dr. Sayer and the group of patients are in the dance hall, he is sitting at a table with a drink. He picks up a cherry that is lying on a napkin near the drink and eats it. One of the female patients asks him to dance, and as he gets up the cherry has reappeared on the napkin.
Continuity mistake: After Dr. Sayer and Leonard get ice cream and go to Dr. Sayer's home, Leonard is sitting on the couch and on the table in front of him is a plate of saltine crackers. The amount of crackers and the way they are lying on the plate change.
Continuity mistake: When Robin Williams leans out of the window, to speak to the nurse who is asking him to go out with her, his shirt is one color/pattern. When the scene shows Robin Williams running out to meet her, his shirt is a totally different color/pattern. Yet the scene does not allow time for a clothing change.
Continuity mistake: When Dr. Sayer is talking to the nurse on the steps at the end of the movie he comes down the stairs with his coat wide open. As he talks to the nurse it is closed if not buttoned. Then when they leave together it is wide open again.
Continuity mistake: When Leonard stays at the hospital instead of going with the group on the bus, he goes to the lunch room and stands in line with the girl he likes. As they are sitting at the table eating, watch the milk glasses on the tray. There is one on the right side of Leonard's tray and one on the left of hers. In the next shot they are both on the right side.