OBJECTIVE: To identify venues with vulnerable populations suitable for testing the community popular opinion leader intervention in each of the five countries (China, India, Peru, Russia, and Zimbabwe) participating in the National Institute of Mental Health (NIMH) Collaborative HIV/STD Prevention Trial. DESIGN: HIV epidemiology and vulnerable populations differ considerably across the countries. Therefore, different community populations were targeted in the five countries. METHODS: Venues and populations were chosen on the basis of specific selection criteria (investigated during the Trial's ethnographic research phase): the willingness of stakeholders and gatekeepers of the venues to cooperate; geographical boundaries defining each venue; population stability within venues; the independence of venues and non-overlap of population members across multiple venues; population size within each venue; social interaction opportunities; and either a high level of sexual risk behavior or a high prevalence of sexually transmitted diseases (STDs) or HIV. RESULTS: Venues and populations selected were food market stall owners and workers in China, male patrons of wine shops and at-risk women congregating near the shops in India, young men and women in social gathering points in neighborhoods in Peru, trade and vocational school dormitory residents in Russia, and people congregating in growth points in Zimbabwe. CONCLUSION: Although the target populations differed across countries, they shared in common high behavioral or biological risk at baseline and suitability for a randomized trial of a community-level HIV/STD prevention behavioral intervention. © 2007 Lippincott Williams & Wilkins, Inc.