Continuity mistake: During the scene where Ness kills the Italian mobster in the lodge near the border, the moment he shoots him the wooden rail behind has two sticks underneath, half a second later, when the mobster is flying backwards dead, the sticks disappear, and a second afterwards, when he is laying dead, the rail's appearance has nothing to do with the previous two.
Continuity mistake: When Gekko says that Ollie is the best trader on the street, Bud turns his head to his right, but when the camera angle changes in the next frame Bud's head is turned to his left. (00:16:00)
Revealing mistake: When Romero gets the harpoon stuck on his chest, he grabs the bulk underneath and you can tell that he squeezes the blood squib to pour the fake blood out.
Other mistake: After Dan visits his wife in the hospital, he goes to Alex's apartment. In the scene where he's chasing Alex and crashes into the glass door, shattering it, look closely at his face and you'll see it's not Michael Douglas but a stunt double. A few seconds later when they are struggling in the kitchen, look again and you'll see the same stunt double.
Continuity mistake: When Jamie gets out of her car, her leg warmers reach down to her heels. In the next shot, they've been pulled up to just her ankles. (00:07:05)
Revealing mistake: When Paul Kersey blows up the restaurant, there are obvious dummies in the booth. (00:46:01)
Continuity mistake: Early in the movie, Mac throws the dead green berets' dog tags to Dutch. As he catches them, Dutch has his hand closed in a fist, and the dog tags are hanging to the left. But in the close-up shot where we can read the name, his fingers are more open, with the tags resting in his palm.
Continuity mistake: When Molly Ringwald is on the phone at the club and gets approached by the girl in orange, throughout the whole conversation the position of the phone receiver in Randy's hand is wildly inconsistent. (00:09:30 - 00:11:00)