Revealing mistake: In the scene where Karen is too afraid to accept free clothes from Jimmy and speeds off, the yellow NY state license plate falls from the parked car to reveal the modern white one underneath.
Continuity mistake: When Jimmy and Henry are talking to Morrie and the camera angle is behind Morrie you can see him holding the phone at his shoulder, when the camera angle switches he has the phone at his ear. Then the phone suddenly disappears when you can see both of his hands and then it comes back again right before Jimmy strangles him with it.
Continuity mistake: In the scene where Pauly talks to Henry and the restaurant owner about Henry's possible involvement in the restaurant biz, Pauly is talking (with the cigar clearly in his hand and it cuts away to him saying "No?" with the cigar jammed directly in his mouth.
Continuity mistake: When Tommy shoots Spider in the foot and he goes down, Henry is playing cards at the table, then in the next scene Henry is helping Spider up, then the very next scene Henry is back at the table watching Spider crawl on the floor.
Factual error: Early in the film, when Henry Hill is selling Pall Mall cigarettes out of a car trunk and is arrested, there are UPC price codes visible on the cartons of cigarettes. UPC codes were not used on products in the 1950's when the scene is taking place. They were introduced in the mid 1970s.
Continuity mistake: Whilst Jimmy is choking Morrie in the wig store the phone suddenly rings and the shot changes. Between shots the way Morrie is standing has all of a sudden changed. Instead of leaning back, he is bent forward. The way he is holding the phone whilst being choked changes as well.
Continuity mistake: When Henry is in prison and he comes in to the kitchen with food in a bag, he first passes some bread to Paul. In one shot he picks up 2 jars and a bottle of wine. The next shot he is carrying the same food but suddenly has a loaf of bread in his hands. When the camera angle switches we now see Henry in front of the table about to sit at the table but now has no food in his arms.
Continuity mistake: When Henry has just shown De Niro the guns and he returns to his car, you see him light up a cigarette. When the shot changes the cigarette has vanished.
Continuity mistake: When Ray's girlfriend is showing off her apartment to her two girlfriends they walk down the hall to the bedroom. The camera then changes to them entering the bedroom door and the order of girls has changed.
Continuity mistake: Henry and Jimmy are eating in a diner waiting for word about Tommy being "made". When Jimmy goes outside to make the call to find out, there is a car parked outside the diner, at this point, the car's window is open. When Jimmy starts kicking over the phonebooth and Henry comes outside to join him, the car's window is closed.