Eighty male and female heterosexual adolescents completed a questionnaire concerning sexual behavior and condom use, AIDS knowledge, ability to communicate with sexual partners about AIDS related issues, and communication with parents about sex and AIDS. Adolescents' perceived ability to communicate with partners about AIDS was the strongest predictor of self-reported condom use. Adolescents' AIDS knowledge did not add predictive power to the relation between communication ability and condom use. Differential effects were found for prior experience in discussing sensitive matters with parents: adolescents who had discussed general sexual issues with parents felt more competent to talk about AIDS with their sexual partners, whereas those who had discussed AIDS with parents felt less competent. The findings imply that knowledge about AIDS is not, by itself, an effective deterrent to unsafe sexual practice among adolescents but is part of a practical know-how about AIDS that also includes specific communication abilities.