The prevention of the spread of acquired immunodeficiency syndrome (AIDS) depends on an educated public reducing their risk of infection. To test the hypothesis that effective community AIDS education can be based in an emergency department, we designed and evaluated two educational interventions in a high-volume urban ED. A pretest/post-test design was used in which subjects were assigned to receive either an active education program, a passive education program, or no education program. Knowledge gains and self-reported risk-reduction behavior were evaluated by follow-up testing within a five-week period. The active and passive groups had significantly greater knowledge gains than the control group (P less than .001). Significantly greater reported reductions in high-risk behavior were found in both the active and passive groups compared with the control group (P less than .01). This study demonstrates that an ED-based AIDS education program can have a significant impact on improving knowledge and reducing self-reported risk behaviors.