For the first time, the Prevagay study was conducted in Lyon, with the primary objective of estimating HIV prevalence among men who have sex with men (MSM) frequenting gay social venues in that city and describing the characteristics of MSM infected with HIV. The study was conducted using a cross-sectional, anonymous, and random approach among MSM frequenting bars, saunas, and backrooms in Lyon, as well as in Paris, Lille, Nice, and Montpellier. Behavioral data were collected via questionnaire, along with blood samples collected on filter paper. HIV antibody testing was performed by the National HIV Reference Center. Among the positive samples, viral load testing and antiretroviral treatment status were assessed. In Lyon, 485 MSM frequenting the 14 venues investigated agreed to participate. Half of them were under 33 years of age. More than 80% identified as homosexual. Nearly 45% had had more than 10 sexual partners in the past 12 months. As in other cities, the lack of condom use was significant and more pronounced among HIV-positive MSM. HIV prevalence was estimated at 11.4% [95% CI: 6.9–18.3]. This proportion was not significantly different from that observed in other cities. Among HIV-positive MSM, 96% had been diagnosed, 83% of whom were on antiretroviral therapy. These results support the need to strengthen the promotion of various protection methods as part of a diversified prevention strategy during outreach activities in gay social venues.