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.
Other mistake: In the scene after De Niro's car explodes, they show him being put in the ambulance feet first. Patients are always put in head first.
Continuity mistake: When Ginger is arguing with the gambler at the craps table about "giving her a bigger cut", the man reaches for her purse to show her the chips she's been stealing from him. As she pulls the purse back, the gold chain strap breaks. The next shot of Ginger shows a repaired chain.
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...
Audio problem: Ace yells "come with me now" over and over while dragging Ginger out of the house after overhearing her trying to have him whacked. DeNiro's lips are not moving while he's yelling.
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: 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: 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?
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.
Continuity mistake: When Nicky goes to Sam's house to meet with Charlie, it's very light outside when he arrives. However when he leaves about four minutes later, the sun is setting. His entire stay at the house takes place during that scene.
Character mistake: When the high roller Ikachawa returns to The Tangiers, Rothstein said he's betting $1,000 instead of his usual $30,000, so when he won, it didn't feel like he had won $10,000 (10 $1,000 bets), but felt like he lost $90,000, alluding to the fact that betting 1/30th of his normal bets made him feel even though he was winning $1k a hand he was missing out on the other $29k, or losing that. At ten hands won, at $1k/hand, he really would have felt like he was losing $290,000, not $90,000 as Rothstein says.