The current study examined the hypothesis that adolescents' absolute and comparative perceptions of vulnerability to potential negative consequences of substance use mediate the relation between traditional predictors of use, and actual substance use. The data support the hypothesis in that absolute risk perceptions mediate the relations between parental communication about substances, peer substance use and risk-taking tendency, and subsequent adolescent use. Comparative risk perceptions, however, are only weakly related to these three predictors, and do not predict subsequent use. The data also replicate earlier findings that behavioral willingness mediates the relation between risk perceptions and behavior. Methodological and applied implications are discussed.