Abstract
Scenario and cost-effectiveness analyses were used to estimate the effectiveness and efficiency of HIV prevention activities in the USA (1978-2000). Under four conservative scenarios on the course of HIV epidemic that might have occurred had there been no prevention efforts. we estimate that prevention activities averted 204,000-1,585,000 infections at a cost of between 49,700 US dollars and 6400 US dollars per infection prevented (less than the medical costs of treating a case of HIV disease).