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. (00:38:30)
Other mistake: In the scene where Jimmy and Henry try to strangle Maury with the telephone cord, the handset is off the hook, but the telephone still somehow rings.
Continuity mistake: When Henry is in prison, Karen comes to visit him and drop off goods she smuggled in. They begin to argue while Henry is holding his daughter and Karen starts placing all the goods on the table. The camera angle switches to just a view of Henry's hands gathering the goods and if you look carefully, you will notice that BOTH of Henry's hands are collecting the goods. This would be impossible considering he is holding his daughter in one of his arms. Once the goods are collected, Henry is seen holding his daughter again.
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. (01:51:35)
Revealing mistake: Morrie gets whacked by Tommy with an ice pick. After that, Morrie is dead and lifeless. Soon after, Frankie Carbone (post Jimmy leaving) exits the car. When he does,the car light comes on and you can see Morrie blink. (01:45:40)
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. (01:54:45)
Visible crew/equipment: When Henry comes out of jail and hugs his wife a boom mike is reflected on the glass of the car door.
Continuity mistake: When Paulie and the others are in prison and preparing dinner, there is a vase on the table where they will eventually eat dinner. The vase is filled with fresh basil at the beginning of this scene but disappears and re-appears throughout the scene.
Continuity mistake: In the scene when Spider is killed by Tommy, Jimmy is with his arms wide open just the instant before Tommy pulls the trigger. But in the next shot, when Tommy fires the gun, Jimmy is with his arms down.
Continuity mistake: In the scene near the end, when the FBI agent is explaining the Witness Protection Program to Henry and Karen, the hemline of Karen's dress changes from one shot to the next. First it's down low on her calf, then it's up by her knee, then it's down again, then up, then down again.
Factual error: When Henry and Karen are racing to Karen's mother's house when the helicopter is following them, the driveway Henry pulls up in has a 1982 or newer Pontiac Bonneville, but the scene was supposed to take place in 1980.
Audio problem: In the bar scene where Tommy gets enraged at Billy Batts, at one point Billy says "Salute Tommy" but his lips do not move.