We examined whether men who have sex with men (MSM) in France have adopted serosorting with their casual partners, serosorting being one strategy to reduce the risk of HIV transmission. We expected to see the same predictors of this practice with casual partners in France as in other similar MSM communities (HIV-seropositive, Internet dating). Data from a cross-sectional survey was used, based on a self-administered questionnaire conducted among readers of the gay press and users of gay websites in 2004. The study population consisted of MSM who reported their HIV status, as well as the practice of unprotected anal intercourse (UAI) with a casual partner at least once during the previous 12 months. Among 881 respondents included in the analysis, 195 (22%) had practiced serosorting: 14% among HIV-seropositive men and 26% among HIV-seronegative men. Serosorting was independently associated with the use of cruising venues (AOR 0.28, p=0.001) and Internet dating (AOR 2.16, p=0.051) among HIV-seropositive men, whereas it was independently associated with the use of cruising venues (AOR 0.59, p=0.013) and the fact of having less partners (AOR 1.50, p=0.046) among HIV-seronegative men. Serosorting requires an up-to-date knowledge of HIV serostatus for MSM and their UAI casual partners, and does not prevent from acquiring other sexually transmitted infections. Prevention campaigns are needed to underline the risks associated with serosorting.