In Phnom Penh, Cambodia, MSM are at high risk of HIV infection because of a significant proportion that reported unprotected anal intercourse and multiple sexual partners. A large proportion of MSM were also found to have penetrative sex with both males and females. This indicates that MSM could be serving as a "bridge group" of HIV transmission to the general population. It can be concluded that male-to-male sexual behavior, which is often of a hidden nature, does represent a link in the spread of HIV and STIs in Cambodia. But more research is necessary to (1) determine the size of the MSM population in both Phnom Penh and other parts of the country; (2) understand the possible contribution of this high risk population to the continued spread of HIV and the scale of resources needed to successfully reach MSM with interventions; and (3) provide more knowledge about other MSM sub-populations not included in this study, such as youth and some clients of male sex workers.