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. (01:05:00)