The impact of the acquired immunodeficiency syndrome (AIDS) epidemic on a group of adolescents was investigated by surveying 197 sexually active, predominantly African-American, urban high school students. Reported sexual behavior changes were evaluated in relation to AIDS-related knowledge and attitudes. Over 50% of the students decreased their frequency of sexual activity, increased their condom use, and/or decreased their number of partners. These students had significantly higher scores on a measure of worry about vulnerability to human immunodeficiency virus (HIV) infection than those whose behavior had not changed. AIDS knowledge, AIDS beliefs, and AIDS-related anxiety interacted with gender to affect sexual behavior change. Male students reporting decreased frequency of sexual activity, for example, had more accurate beliefs about AIDS than males reporting no decrease. Among female students, however, those reporting decreased frequency had less accurate beliefs than those reporting no decrease. These results highlight the importance of considering gender and specific sexual behaviors when designing AIDS education interventions.