 From 2000 to 2004, we assessed the seroprevalence of Entamoeba histolytica infection using indirect hemagglutination antibody IHA assay among 667 HIV-infected persons group 1, 1311 asymptomatic HIV-uninfected persons seeking anonymous HIV testing group 2, 616 HIV-uninfected controls with gastrointestinal symptoms diarrhea andor liver abscess seeking medical care group 3, and 2500 healthy controls undergoing health check-up group 4. An IHA titer greater than 128 was detected in 7.1 of group 1, 2.5 of group 2, 1.8 of group 3, and 0.1 of group 4 p0.0001. The highest seroprevalence 11.2 was noted among HIV-infected persons who were MSM aged 30 to 39 years. Compared with persons with gastrointestinal symptoms, the adjusted odds ratio for having high IHA titers among HIV-infected persons was 3.206 95 confidence interval, 1.433, 7.176 p0.005. These findings demonstrate that HIV-infected persons, especially MSM aged 30 to 39 years, are at significantly higher risk of E. histolytica infection. 