Continuity mistake: At the end of the movie when the Lutzs' get in their van and drive off; they stop near a dead end sign when George gets out and goes back to get Harry. When he and Harry get back to the van and drive off, the van is farther from the dead end sign than it were before. (01:51:45 - 01:55:25)
Continuity mistake: When George stops the van and runs to the house, you see a long distance shot of the van as George gets out. Later on, when George falls in the black/red sludge under the stairs and the shot switches to the van again, it is the exact same shot as before. Right before the shot switches to the family in the van, you can actually see the van driver-side door opening as George gets out. (01:52:05 - 01:53:05)
Continuity mistake: When it shows the front door, the structure of the door changes throughout the film.
Continuity mistake: In the beginning, when it shows the outside of the house, we hear Ronald DeFeo killing his family with a gun. But during the house tour, when it shows the murders from the inside point of view, the number of gunshots fired is different than when we heard it from the outside of the house.