Abstract Background High rates of bacterial STIs have been reported in high-risk MSM receiving tenofovir/emtricitaine (TDF/FTC) pre-exposure prophylaxis against HIV (PrEP) in clinical trials. However, systematic screening for STIs may amplify the diagnosis of asymptomatic infections in this population. We report the results of STI incidence in MSM enrolled in a PrEP program in Lyon University Hospital, France. Methods All patients addressed for PrEP in the department were enrolled. Baseline assessment included HIV serology, serum creatinine and STI screening (syphilis, HAV, HBV and HCV serology and N. gonorrheae/C. trachomatis PCR assay on urine, anal and pharyngeal swabs). HIV test, creatinine, bacterial STIs and HCV screening were repeated every 3 months. Incidence rates were determined per 100 patient-year (/100PY). Results From January to September 2016, 211 patients were enrolled. All patients were MSM reporting unprotected anal sex (median age 36.4 years). Median condom use was 50%. 6% were escorts or prostitutes, 46% participate in sex parties, 53% used chemsex. Nine patients did not start PrEP, including 3 patients with HIV primary infection at baseline. 32 patients were lost to follow-up (FU). Median FU was 6.3 months for the remaining 170 patients (97 PY). No patient acquired HIV and 3 patients had acute HCV during FU. Conclusion A high prevalence and incidence of bacterial STIs were observed in high-risk MSM engaged in a PrEP program. All prevalent STIs and 80.3% of incident STIs were asymptomatic. Frequent screening and treatment of asymptomatic STI are warranted to reduce the spread of STIs in this population. STI history (%) Baseline prevalence(% symptomatic) Incidence rate /100PY(% symptomatic) Syphilis 37.9 3.8 (0) 14.8 (18.7) N. gonorrheae 48.2 7.6 (0) 58.7 (22.5) Pharyngeal 3.9 (0) 22.5 (0) Urine 1.0 (0) 12.0 (41.2) Anal 3.9 (0) 34.4 (25.0) C. trachomatis 40.5 7.6 (0) 47.6 (16.0) Pharyngeal 1.0 (0) 9.6 (0) Urine 1.0 (0) 8.4 (30.0) Anal 5.8 (0) 33.5 (15.6) All bacterial STIs 74.2 16.3 (0) 86.9 (19.7) Disclosures L. Cotte, GILEAD: Scientific Advisor, Consulting fee