Successful recruitment and retention of HIV-uninfected at-risk participants are essential for HIV vaccine efficacy trials. A multicountry vaccine preparedness study was started in 2003 to assess enrollment and retention of HIV-negative high-risk participants and to assess their willingness to participate in future vaccine efficacy trials. HIV-negative high-risk adults were recruited in the Caribbean, in Southern Africa, and in Latin America, and were followed for 1 year. Participants included men who have sex with men, heterosexual men and women, and female sex workers. History of sexually transmitted infections and sexual risk behaviors were recorded with HIV testing at 0, 6, and 12 months, and willingness to participate in future vaccine trials was recorded at 0 and 12 months. Recruitment, retention, and willingness to participate in future trials were excellent at 3 of the 6 sites, with consistent declines in risk behaviors across cohorts over time. Although not powered to measure seroincidence, HIV seroincidence rates per 100 person-years (95% confidence interval [CI]) were as follows: 2.3 (95% CI: 0.3 to 8.2) in Botswana, 0.5 (95% CI: 0 to 2.9) in the Dominican Republic, and 3.1 (95% CI: 1.1 to 6.8) in Peru. The HIV Vaccine Trials Network 903 study helped to develop clinical trial site capacity, with a focus on recruitment and retention of high-risk women in the Americas, and improved network and site expertise about large-scale HIV vaccine efficacy trials.