This study examines the influence of perceived risks as well as the understudied role of benefits on alcohol and marijuana use among adolescents and adults. Ninth grade students and young adults were asked about the perceived risks and benefits of alcohol and marijuana use. Analyses showed a consistent pattern: perceived benefits were more predictive of actual drinking and intentions to smoke marijuana, over and above perceived risks, previous experience, and age. Implications for policy from these findings are highlighted. (Contains 14 charts.) (GCP)