A cross-sectional survey, using self-sampled finger-prick blood on blotting paper and anonymous behavioral self-administrated questionnaires was conducted in Paris in 2009 among MSM attending gay venues. Paired biological results and questionnaires were available for 886 participants. HIV seroprevalence was 17.7 % (95 % CI: 15.3-20.4). Four groups were identified according to their knowledge of their HIV biological status. Among the 157 found to be seropositive, 31 (19.7 %) were unaware of their status and reported high levels of sexual risk behaviors and frequent HIV testing in the previous 12 months. Among the 729 MSM diagnosed HIV-negative, 183 were no longer sure whether they were still HIV-negative, or had never been tested despite the fact that they engaged in at-risk sexual behaviors. This study provides the first estimate of HIV seroprevalence among MSM in Paris and underlines the specific need for combined prevention of HIV infection in this MSM population.