The Centers for Disease Control and Prevention, in collaboration with 25 state and local health departments, began the National HIV Behavioral Surveillance System (NHBS) in 2003. The system focuses on people at risk for HIV infection and surveys the three populations at highest risk for HIV in the United States: men who have sex with men, injecting drug users, and high-risk heterosexuals. The project collects information from these three populations during rotating 12-month cycles. Methods for recruiting participants vary for each at-risk population, but NHBS uses a standardized protocol and core questionnaire for each cycle. Participating health departments tailor their questionnaire to collect information about specific prevention programs offered in their geographic area and to address local data needs. Data collected from NHBS will be used to describe trends in key behavioral risk indicators and evaluate current HIV prevention programs. This information in turn can be used to identify gaps in prevention services and target new prevention activities with the goal of reducing new HIV infections in the United States.