Ample studies have established that parents as well as peers function as role models in the development of adolescents' alcohol use. The role of siblings, however, has been largely neglected despite the long-term nature of a sibling relationship. The present study examined the impact of siblings on drinking behavior of adolescents using longitudinal data from 416 sibling dyads. Moreover, we explored which factors (gender constellation of the sibling dyad, quality of the sibling relationship, and similarity in norms about alcohol) affect reciprocal influences in alcohol use of siblings. Descriptive analyses showed that although older siblings drink more frequently and intensively than the younger siblings, moderate associations were found between frequency and intensity of drinking in siblings. Findings of structural equation modeling demonstrated that alcohol use of the older sibling marginally affected drinking of the younger sibling one year later. Drinking of the younger sibling did not affect drinking of the older sibling. Further, we found no moderating effects of having the same or opposite gender as a sibling, a low or high quality relationship, and the same or different norms about alcohol, on the association between siblings' alcohol use and adolescents' drinking over time.