Continuity mistake: When DeNiro catches the cheats at the card tables, he takes the one with the beard to smash his hand with a hammer. In the first shot the guard is holding the cheat down by the wrist, but in the next shot the guard's hand is up by the guy's elbow.
Factual error: When Joe Pesci is driving to meet De Niro, he has to change cars. The scene right before going to the garage, they show Pesci's car driving around a corner and at the bottom right of the screen, you see a lamp post with a bus sign on it that reads CAT. CAT (Citizen's Area Transit) wasn't established in Las Vegas until late 80's early 90's. Before that it was the Las Vegas Transit. This scene was supposed to be late 70's, early 80's...
Continuity mistake: In the scene towards the end before De Niro's car explodes, in the first shot when he opens the door its window is down as he gets in the car, but in the next shot as his motions are replayed, when he opens the door that window is all the way up, then it's down again in following shots. (02:46:00)
Continuity mistake: Jennifer has the diamonds inside her hair bun and she's shaking it to retrieve the diamonds onto the table. As Santoro slaps her face as a gesture to thank her and for her not to get smart with him, her hair bun comes loose and falls out into a pony tail. The next shot then shows Jennifer with the hair bun perfectly groomed again on top of her head.
Continuity mistake: When Nicky has the guy's head in a vise, after it squirts Nicky's hair changes between shots, from neat to messed up.
Continuity mistake: Towards the end of the movie, when they first kill Nicky's brother, Dominick, and they throw him in the pit, his full chest is covered in blood, but in the aerial shot it is clean with just the bloody face.
Continuity mistake: When news on Robert De Niro not having a casino license first hits the airwaves, the news broadcast displays a still picture of Joe Pesci having a conversation with his friend Frankie. The picture that they use is when Pesci and Frankie have tooth picks in their mouths because they don't want FBI agents lip reading what they are saying. But that didn't happen until later on in the movie. So how could they have displayed a picture of a conversation that hadn't taken place yet?
Factual error: We hear Ace in the voiceover talking about Ichikawa, a guest at Tangiers, and Ace says, "About a year ago, he cleaned out a couple of casinos in the Cayman Islands." There have never been casinos in the Caymans. (00:19:10)
Continuity mistake: When Ace is having a meeting with Green about him firing the cowboy, Ace stubs out his cigarette. In the next shot from behind Ace is still smoking, but when in the front he has no cigarette.