This study examined the relations between risk cognitions and risk behavior. Adolescents’ perceptions of the risks associated with driving after drinking (DAD) and their perceptions of the prevalence of this behavior among their peers were assessed, and these perceptions were used to predict their DAD behavior. Results provided evidence of a type of cognitive social influence: the more common adolescents thought the behavior was, the less risk, both personal and general, they attributed to it. As expected, however, this relation was significant only for those who were high in a tendency to engage in social comparison. Perceptions of risk, in turn, were prospectively related to risk behavior for all participants. Specifically, low perceived risk, especially personal risk, was associated with an increase in DAD behavior. Implications of the results for DAD interventions are discussed.