Sexual transmission of HIV in China is rapidly increasing, in part driven by commercial sex work. This article examines variations in occupational control among one type of brothel-based prostitutes in China, and the relationship between the terms and content of this work and the risk of HIV/AIDS. Organizational factors are discussed as part of the current political, economic, and social context of sex work in China. The analysis is based on ethnographic observation and in-depth interviews conducted in south China in 2000 and 2001 involving 158 female prostitutes from 45 brothels in 4 red light districts. Qualitative analysis of interview and observational data used development of thematic codes measuring occupational control. Brothel-based female sex workers in China are a heterogeneous population, displaying considerable variability in the organization of life and work, relationships with managers and clients, ability to negotiate condom use, knowledge of sexually transmitted diseases and HIV, and occupational identity, all of which may result in different risks of acquiring HIV. HIV prevention activities in China must focus on sociocultural aspects of sex work. Such interventions depend on detailed knowledge of its organization. The results of this study demonstrate the importance of prevention activities directed at the brothel managers and clients, as well as the sex workers.