China is the next probable frontier for the global HIV epidemic. Central to this anticipated growth of the epidemic is the nation's new and growing population of rural-to-urban migrants. Although there are an estimated 120 million migrants, little information is available about their social and cultural context of their lives in urban areas and their HIV-related perceptions and behaviors. On the basis of the in-depth individual interviews conducted among 90 rural-to-urban migrants in 2 major Chinese cities, Beijing and Nanjing, this qualitative study was designed to explore these issues with a particular focus on their relevance to sexual transmission of HIV. The findings suggest an urgent need for HIV/STI prevention programs that address the cultural, social, and economic constraints facing the migrant population in China.