John Ottman's score was originally used during the trailer, however his score was rejected shortly before the film was released and was replaced by Ed Shearmur.
Porn star Alisha Klass appeared as a cheerleader, but her brief scene was cut. You can see a glimpse of her in the lower right hand part of the screen when Sebastian is talking to Annette on the phone.
The scene in which Annette slaps Sebastian was also unscripted. Reese Witherspoon and Ryan Phillippe were so into their scene that she slapped him unexpectedly, and Phillippe's reaction is genuine. He was so into the scene that right after the director said cut, he went behind the set and threw up. The director left the scene in the final cut.
Despite previous reports, Reese Witherspoon was not pregnant during filming. The movie filmed from 9 June 1998 - 15 July 1998, and Witherspoon had her daughter Ava on 9 September 1999. A full year after filming the movie. She was, however, pregnant, when they did the press tours for the film.
The kissing scene between Sarah Michelle Gellar and Selma Blair, ranked the film at #32 on Entertainment Weekly's "The 50 Sexiest Movies Ever" (issue #1023, November 28, 2008).
Although Sarah Michelle Gellar plays the older version of Kathryn while Amy Adams plays the younger version in the prequel Cruel Intentions 2, in real life Sarah Michelle Gellar is younger than Amy Adams by 3 years.
The trivia items below may give away important plot points.
Toward the end of the film when Kathryn tells Ronald that Sebastian had hit her, the actual scene of Sebastian striking her was filmed, but it was deleted because the dialogue from Sebastian during this part didn't fit his character.
One version of Roger Kumble's screenplay had an ending where Annette, instead of publishing the journal and crushing Kathryn, keeps it to herself and announces her cruel intentions to play games on Kathryn under the threat of revealing the contents.
After her public humiliation, Kathryn Merteuil's cross gets pulled open and her cocaine falls out, referencing the scene in Dangerous Liaisons in which the similarly disgraced Marquise de Merteuil (Glenn Close) sweeps a cloud of white powder off her dressing table.