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: 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 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: 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.
Visible crew/equipment: When Chrissie gets knocked out by the plant pot, you can see a safety mat conveniently placed next to her.