Men who have sex with men (MSM) in Vietnam's urban centers are increasing in numbers and visibility. Although limited to a few surveys, the available data on MSM in Vietnam show that they are at increased risk for HIV infection due to high numbers of sexual partners, high rates of unsafe sex, and inconsistent condom use. There are significant numbers of male sex workers in Vietnam and these men are also at high risk for HIV infection. The lack of data on HIV prevalence among MSM and the fact that the media and public health prevention programs ignore MSM as a population at risk leads many MSM to mistakenly believe that their risk for HIV is low. The low perception of risk, combined with inadequate knowledge, may make MSM less likely to actively protect themselves from HIV infection. More research is needed on current behavior and HIV prevalence among MSM and male sex workers in Vietnam. MSM in Vietnam's larger cities could easily be targeted for prevention using peer educators to decrease their risk for HIV infection.