The human immunodeficiency virus (HIV)/AIDS epidemic is currently spreading faster in Cambodia than anywhere else in Asia. Heterosexual transmission of HIV through prostitution is believed to be catalyzing the epidemic, and sex workers (SWs) are at a very high risk for becoming infected with HIV and subsequently developing AIDS. In order to gain a better understanding of the knowledge, attitudes and practices of this highly vulnerable population, face-to-face interviews were conducted with SWs (N = 502) in the capital city, Phnom Penh. The SWs surveyed were predominantly young, uneducated, poor women from rural areas, many of whom remain isolated in brothels. Brothel-based SWs are probably at greatest risk for acquiring HIV. They reported twice as many sexual contacts per day and used condoms less frequently than community-based SWs. The majority of SWs surveyed knew that condoms offered protection against HIV/AIDS, although one-quarter of SWs did not always use condoms. Despite their high level of baseline HIV/AIDS knowledge, nearly all SWs requested that additional health education materials be made available to them and their customers.