BACKGROUND: Human immunodeficiency virus (HIV) and sexually transmitted infections (STI) are prevalent among men who have sex with men (MSM). GOAL:: To estimate the prevalence of HIV and STIs in this group. STUDY: A total of 694 MSM were tested for HIV, hepatitis B (HBV), hepatitis C (HCV), human T-cell lymphotropic (HTLV-I/II) viruses and Treponema pallidum infection. RESULTS: HIV, HBV, and T pallidum were detected in 13.8%, 37.7%, and 16.9% of subjects, respectively. Prevalences of 1.9% and 0.3% were detected for HCV and HTLV-I/II. A prior history of STI was the most predictor for HIV, HBV, and T pallidum. Use of illegal drugs, blood transfusion history, and multiple sexual partners were associated with HCV. The 2 most common coinfections were HBV/T pallidum and HIV/HBV. CONCLUSIONS: Infection with HIV, HBV, and T pallidum was elevated among MSM. Routine testing, education, vaccine-based prevention, and control programs need to be implemented in this high-risk population. Copyright © 2006, American Sexually Transmitted Diseases Association All rights reserved.