Continuity mistake: When the stairs are first shown, there's carpet up the middle of the stairs. At the end when they flee the house it's gone.
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)
Revealing mistake: You can see Jackie's knuckles are already bloody BEFORE she starts pounding on the closet door.
Other mistake: When George is in the basement, his son starts walking down the stairs. Suddenly a light bulb shatters right next to the boy's head, he screams, and falls violently down the stairs. But when it cuts to George coming over, he's just walking at a normal pace as though nothing happened. (This is just after they move in, before the evil spirits take hold of George, so there's no reason for him not to be alarmed.).
Character mistake: When Jackie the babysitter is stuck in the closet, she explains to George and Kathy that the door was locked. George says Amy there's no lock on this door. Her real name is Amy and her film name is Jackie.
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.
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.
Revealing mistake: When the lady is showing George and Kathy the kitchen, she casts two shadows because of the stage lights above her head.
Revealing mistake: When Matthew and Gregory go downstairs to answer the door, it's aunt Helena. Right before she pinches Matthew's cheek, you can see it's already red from a previous take.