Continuity: When Dahmer is attacking his first (chronological) victim, Dahmer's left hand is alternately grasping/not clasping his victim's jersey between shots.
Continuity: When Rodney falls while dancing with the skeleton first it's on top of them, then to his side, and then on top of him again.
Continuity: When Lance is on top of Jeffrey and choking him, his hand changes position on Dahmer's neck between shots.
Continuity: When Rodney is seducing Dahmer, and draping the belt around his neck, the buckle moves from the left and right side of his neck between shots.
Continuity: When Dahmer is sitting in the lunch room of the chocolate factory, the establishing shot shows three chocolate men standing in a row in front of him. In the next shot, the chocolate figure on the right has fallen down.
Audio/visual unsynchronized: At the end when Dahmer and Rodney are fighting, Rodney's wife beater changes from white to red and back to white again.
Anachronisms: When Dahmer gets pulled over by the cop in 1978, he shows a New York State driver's license from post 1995.
Factual errors: The uniforms for the Milwaukee Police officers are incorrect. The badges and cap shields are L.A. style and the officers are wearing shoulder patches on both shoulders. Milwaukee officers wear a patch only on the left shoulder.
Anachronisms: The film depicts Milwaukee Police in a black and white car. Milwaukee police at that time drove solid white cars and did not go to black and white until 2008.
Boom mic visible: During the scene where Jeffrey is about to purchase a knife in the sporting goods store, a boom microphone is visible at the top-center of the screen. This occurs right after the store clerk says "I ain't even messin' it up."