Continuity mistake: When Dr. Ross and Bruce are in the hotel room, Banner empties the purse on the bed and there is some cash inside the wallet. As they are about to leave he picks up the cash, which isn't in the wallet anymore. (01:08:10)
Continuity mistake: During the street chase in Brazil, the time of day changes from night, to perhaps late afternoon/evening, to night again.
Revealing mistake: When the Hulk walks through the stream, the water doesn't react to his feet. (00:59:20)
Continuity mistake: At the beginning of the movie, when the general wears his dress greens, his epaulet rank has the stripe near his neck. Later,in a shot about halfway through, the stripe is near his shoulder.
Continuity mistake: As Emil is in the men's restroom looking at the mirror, some of his hair is hanging over his forehead, but when the shot changes, his hair is suddenly brushed back.
Continuity mistake: When Bruce and Betty are hugging on the bridge, they turn back and forth about a quarter of a turn whenever the camera angle changes.
Factual error: When the police are searching for abomination in New York City, they reach an alleyway where there's a police car marked 'Toronto Police'.
Continuity mistake: When Hulk throws the chunk of sheet metal at the helicopter, it glances off the rotor housing (taking a ragged piece with it.) When the chopper crashes, however, the propeller comes off with a perfectly clean edge, as if the projectile had sheared completely through the base.
Factual error: The USB drive should have been destroyed after sitting in Bruce's stomach for a day, or at least been somewhere in his intestines, so he wouldn't have been able to puke it up.
Continuity mistake: After the first time we see Bruce transform into the Hulk, he has hitched a ride with the elderly man. You will remember he has 3 1/4 length pants on with a few rips. It cuts to a quick clip of him walking up the road but this time he has full length pants on. They switch back to shorter length pants straight after.
Other mistake: Bruce is seen wearing a Polar F5 heart rate monitor in a couple of scenes after Betty gives it to him (such as when he is in bed with Betty) but there is no transmitter strap around his chest, which that model needs in order to pick up the wearer's heart rate.
Revealing mistake: In the beginning of the film, Bruce Banner's hair is a dark brown and looks natural. When he is doing the anger control exercises, he is obviously wearing a black wig which is not natural looking at all. This happens a few times during the movie - it switches from his natural hair to the very dark wig. And at times, even his eyebrows look much darker and thicker.
Continuity mistake: When Dr. Ross empties her handbag on the bed, there is a Givenchy compact with the Givenchy insignia face up. When the bed is shown again, the compact is face down.
Factual error: Near the start of the movie, in Brazil, Bruce is studying Portuguese but the people are speaking Spanish. Brazilians speak Portuguese.
Factual error: When Blonsky is seen wearing the American Class A uniform, it's visible he has not shaved his face for days. Quite unthinkable for the military - be it American or British. If he had time to change from his BDUs to the Class A uniform then he would have had time to shave as well. Soldiers in Iraq aren't even excused from shaving daily unless they have a medical condition that prevents them from shaving.