Continuity mistake: In the final scene where Annette is driving the Jaguar and having flashbacks, watch as she drives past lovely rolling hills and pastures. Cut to a helicopter shot of her driving the car along a New York freeway (FDR I think...) This mistake has been confirmed by the director.
Continuity mistake: When Sebastian goes to visit Blaine, Blaine is using a scale to weigh out some marijuana. In one shot, there is a big pile on the scale, the camera cuts away. When the camera comes back to Blaine, there is a much smaller pile of marijuana. The camera cuts away and back again...the big pile has reappeared.
Continuity mistake: In the end when Kathryn receives a copy of Sebastian's journal, the title page reads, "Cruel Intentions". When several moments later, just before the headmaster takes the crucifix and opens it, the camera pans across the journal in her hands, the title now reads "Cruel Inventions".
Continuity mistake: When Sebastian is explaining to Kathryn that he had the chance to sleep with Annette but he didn't, he is lying on the bed with Kathryn straddling him. Then he gets up and pushes her over. When the camera switches to a different view of her, her legs and arms are in different positions than they were before.