Objective To determine the prevalence of and correlations between HIV infection and syphilis among men who have sex with men (MSM) in Beijing.Methods Totally,600 MSM collected from sentinel surveillance sites for AIDS in Beijing were recruited in this study,and underwent screening tests for HIV infection and syphilis.Enzyme-linked immunosorbent assay (ELISA) was used for the primary screening for HIV infection,and Western blot for its confirmation.Both nontreponemal test (rapid plasma regain (RPR) assay) and treponemal test (Treponema pallidum particle agglutination assay,TPPA) were performed to detect syphilis,and only those with a reactive TPPA result were defined as having syphilis (including past infection).Specimens confirmed as HIV-1 positive were further tested with BED-capture enzyme immunoassay (CEIA) to find recent HIV-1 infection,and the incidence of HIV infection was then calculated.The correlation between syphilis and HIV infection was statistically analyzed.Results Of the 600 MSM,49 (8.17％) had HIV infection,including 14 cases of recent infection,with the incidence rate of HIV infection being 4.68％; 51 were positive for both RPR and TPPA tests with the infection rate (including past infection) being 18.5％ (111/600).People without a Beijing household registration and those with high education levels accounted for a large proportion of HIV-infected MSM.Conclusions The prevalence and incidence of HIV infection as well as prevalence of syphilis maintain at a relatively high level in MSM in Beijing.HIV infection is markedly correlated with syphilis in MSM population.