Undiagnosed HIV infections contribute disproportionately to the HIV epidemic. We recruited 639 gay men attending social venues, who completed a cross-sectional survey with oral fluid collection for HIV testing in 2008. We calculated HIV and undiagnosed HIV prevalence and used ? 2 tests and logistic regression to examine associations between participant characteristics and HIV status. Among 639 men, 61 (9.5 , 95 confidence interval: 7.4 to 12.1 ) tested HIV positive, of which 19 (31.1 , 95 confidence interval: 19.9 to 44.3 ) were classified as undiagnosed HIV positive. Almost a third of HIV-positive men were unaware of their HIV status, and of these men, a large proportion engaged in high-risk behaviors.