BACKGROUND: Of 2.5 million new HIV infections worldwide in 2007, most occurred in sub-Saharan Africa and southeast Asia. We present the baseline data on HIV risk behaviors and HIV testing in sub-Saharan Africa and northern Thailand from Project Accept, a community-randomized controlled trial of community mobilization, mobile voluntary counseling and testing (VCT), and posttest support services. METHODS: A random household probability sample of individuals aged 18-32 years yielded a sample of 14,657, with response rates ranging from 84%-94% across the 5 sites (Thailand, Zimbabwe, Tanzania, and 2 in South Africa). Individuals completed an interviewer-administered survey on demographic characteristics, HIV risk behaviors, and history of VCT. RESULTS: In multivariate analysis, females, married individuals, less educated with 1 sexual partner in the past 6 months were more likely to have had unprotected intercourse in the previous 6 months. Rates of lifetime HIV testing ranged from 5.4% among males in Zimbabwe to 52.6% among females in Soweto. CONCLUSIONS: Significant risk of HIV acquisition in Project Accept communities exists despite 2 decades of prevention efforts. Low levels of recent HIV testing suggest that increasing awareness of HIV status through accessible VCT services may reduce HIV transmission.