HIV prevention research: accomplishments and challenges for the third decade of AIDS.

The past 2 decades have taught us that HIV prevention can work. We now have evidence from places as diverse as Senegal, Thailand, Uganda, and Australia that concerted HIV prevention efforts at the national level have resulted in the maintenance of low seroprevalence rates where they otherwise would have been expected to rise. We are beginning to observe declining rates of HIV prevalence and incidence in places and populations with historically high rates--for example, injection drug users in New York City. This trend points to the long-term impact of prevention efforts in those communities. The best of these efforts have been based on sound scientific research. As we move into the third decade of the AIDS epidemic, it is important to restate principles, acknowledge advances, and identify challenges and future directions in HIV prevention research.