OBJECTIVES: We investigated involvement and cooperation patterns of local Brazilian AIDS program actors and the consequences of these patterns for program implementation and sustainability. METHODS: We performed a public policy analysis (documentary analysis, direct observation, semistructured interviews of health service and nongovernmental organization [NGO] actors) in 5 towns in 2 states, São Paulo and Pará. RESULTS: Patterns suggested 3 models. In model 1, local government, NGOs, and primary health care services were involved in AIDS programs with satisfactory response to new epidemiological trends but a risk that HIV/AIDS would become low priority. In model 2, mainly because of NGO activism, HIV/AIDS remained an exceptional issue, with limited responses to new epidemiological trends and program sustainability undermined by political instability. In model 3, involvement of public agencies and NGOs was limited, with inadequate response to epidemiological trends and poor mobilization threatening program sustainability. CONCLUSIONS: Within a common national AIDS policy framework, the degree of involvement and cooperation between public and NGO actors deeply impacts population coverage and program sustainability. Specific processes are required to maintain actor mobilization without isolating AIDS programs.