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 χ(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.