Continuity mistake: In the scene where the Asian guy is peeing off Stifler's balcony, he knocks over a plant and knocks out Christy. In the next shot the plant is back, and in the one after that it is gone again.
Revealing mistake: When Jim's Dad walks in on him and the girl having 'goodbye sex', Jim scrambles around trying to cover himself. At one point, as he's going from the floor to the bed, you can see the string bikini or whatever he's wearing so that he doesn't accidentally expose himself.
Continuity mistake: Stifler tries to 'go fishing' for some girls and throws a long bomb to the other guy who falls onto some bikini clad girls having a picnic, as he lands a previously intact Pepsi bottle is suddenly crushed before he even lands on it.
Continuity mistake: At the party at Stifler's the other guys are playing cards at a table and the amount of cards lain down, the numbers and suits of the cards, and the position the cards are in change with every shot, and when the cops show up there are no cards at all on the table.
Visible crew/equipment: Near the end of the film, when the guys are getting into the car, the reflection of the film crew can clearly be seen in the car door.
Continuity mistake: When Jim is back in his bedroom, he looks at the picture of the girl, and between shots it moves slightly in the close up.
Continuity mistake: In the scene where the Asian guy is taking a piss of the balcony at Stifler's party, you see Stifler and his girl stand up when the pee hits the pillow. Then the camera is switched to the balcony where the Asian guy and a girl are talking. Then again we see Stifler and his girlfriend, but now the pillow is dry again.
Continuity mistake: In the lesbian scene, one girl pulls her bra down around her waist. She then pulls it back up over her breasts. In the next shot her bra is back down around her waist. In the following shot the bra is over her breasts.
Deliberate mistake: During the "breaking up" scene with Jim and Michelle when they're inside the cabin, her hair is crimpy, but when she walks outside and gets into her car, her hair is straight. This is because Alyson Hannigan filmed this particular scene during a break in the filming of a "Buffy the Vampire Slayer" episode.
Continuity mistake: When Jim is sitting with his Dad in the waiting room, after he glued himself, he is holding the videotape at an angle which is toward him. The woman in the wheelchair could not possibly see the title of the video but, when they show her noticing it, the tape is being held at an angle facing towards her.
Continuity mistake: In the scene where Stifler is chasing Finch down the stairs at Stifler's party, Jim separates them both while holding a cup in his right hand, which he switches to his left, then in the next shot from a different angle it is back in his right hand.
Continuity mistake: When Oz and Heather try to have phone sex for the second time, there is a pimple on her forehead. After her roommates come in, she sits up and it's gone.
Continuity mistake: After the lesbian scene, when Stifler brings in a box of porno tapes, he tosses a tape to Jim. At one angle, the tape lands towards Jim's feet. In the next angle, the tape lands on Jim's chest.