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
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.
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.
Eva Green's credited film debut. She previously appeared in Michael Haneke's The Piano Teacher (2001) but was uncredited.
Camera operator Luigi Andrei said he was a little embarrassed about filming in this movie: "In one scene I had to bring the camera closer to Eva Green's naked body, or to Louis Garrel's, just at 20/30 cm, and I showed some hesitation in doing so, until Bernardo Bertolucci screamed "Run on those bodies, do not be afraid!". In another scene Michael Pitt kissed all of Eva's naked body, starting from her feet. At that moment I was just stuck to her, and I was running a cart along her body at 20 centimeters, and I really saw everything about her, in the smallest details, almost like I was a gynecologist."