BACKGROUND: It is common knowledge that alcohol use and violence in adolescence is interrelated. However, less is known about variables which modify the link between alcohol use and violent behaviours in adolescence. The present study investigates how the interaction of intraindividual [adolescent risky single occasion drinking (RSOD)], intrafamilial (risky drinking of older siblings) and extrafamilial (risky drinking among peers) alcohol-related risk factors contributes to adolescents' violence and delinquency. METHODS: Multiple linear regression analyses including two- and three-way interactions were conducted based on a national representative sample of 3711 8-10th graders in Switzerland (mean age 15.0, SD = 0.95) who had older siblings. RESULTS: All three alcohol-related risk factors and the three-way interaction contributed significantly to the frequency of violence and delinquency. Adolescents who frequently engage in RSOD and have both drunken peers and drunken older siblings had the highest levels of violence and delinquency. Moreover, their association between own drinking and violence increased the steepest. CONCLUSION: The present study confirmed the occurrence of cumulative risk processes and demonstrated that excessive alcohol consumption among older siblings and peers represents a crucial contextual factor for the link between adolescents' risky drinking and violence and delinquency. For prevention, the findings suggest that a focus on peers alone may not be effective if the familial background is not taken into consideration.