To make the actors feel comfortable and natural in the film's nude scenes, the director Bernardo Bertolucci would encourage them to be totally nude long before the actual shot so they could get used to be naked around each other. Source: Director's commentary on DVD
In order to prevent himself from getting "too excited," Michael Pitt has said he would dip "himself" into a glass of ice water before his graphic love scenes with Eva Green.
Leonardo DiCaprio was offered the role of Matthew, but turned it down because he was in pre-production with The Aviator (2004). Michael Pitt, who bears considerable resemblance to DiCaprio, was cast in his place.
Eva Green's credited film debut. She previously appeared in Michael Haneke's The Piano Teacher (2001) but was uncredited.
There were scenes in the script depicting much more blatant sexual relations between the characters of Matthew and Theo, but they were not filmed. Director Bernardo Bertolucci said, "The gay sex was in the first script, but I had a feeling that it was just too much stuff. It became redundant." Actor Michael Pitt said in an interview, "It was in the script and it's what I'd signed to do. But they said we weren't going to do that."