Jay Hernandez had to learn many of his Spanish lines phonetically because he does not speak fluent Spanish.
Many of the high school scenes were shot at a real high school. The director wanted actual students to be extras in the film. Most of them had no acting experience.
Kirsten Dunst's character Nicole was originally supposed to have a nude scene. In one scene, Nicole leaves the bedroom in a cut off shirt and her underwear and walks into the kitchen past the maid to retrieve some condoms. In the script she was supposed to do this nude. Dunst was 17 when she got cast but would turn 18 by the time she started filming, so she was willing to do it nude because she wanted to break away from the good girl roles she played as a child. But her mother flatly refused to let her. Though she did end up appearing topless with her arm covering her breasts. Five years later, Dunst did have partial nude scenes in Marie Antoinette (2006), and then went topless in Crimen en familia (2010) and fully nude in Melancolía (2011).
Hermosa locura (2001) was originally inspired by a book of Lauren Greenfeld photos called 'Fast Forward.'
The scene in which Nicole buries Carlos in a hole in the sand, with only his head above ground, and takes a picture, the original caption for the photo was "In Nicole's Hole". It was changed to "I Love Nicole" in order to maintain a PG-13 rating.