Adolescents' reckless driving, drinking, and smoking, along with their cognitions about these behaviors, were assessed in a 3-year longitudinal design. Consistent with most models of health behavior, the results indicated that health cognitions predict risk behavior. In addition, the current data demonstrate that increases in risk behavior are accompanied by increase in perceptions of vulnerability and prevalence and by decreases in the influence of concerns about health and safety. Furthermore, the changes in prevalence estimates and concern about health and safety predicted subsequent risk behavior. These results demonstrate reciprocity between risk behaviors and related cognitions and suggest that adolescents are aware of the risks associated with their behavior but modify their thinking about these risks in ways that facilitate continued participation in the behaviors.