Sibling victimization is associated with adjustment problems. Protective factors that reduce the detrimental effects of sibling victimization are unknown. We examined the mediating role of social support from family and friends in the relationship between sibling victimization and adolescents' mental health distress, self-esteem, and delinquency. A telephone survey (N = 850; 49% female) was conducted with a nationally representative sample of United States adolescents (Aged 10 to 17). Three mediation models were tested exploring (a) the unique effects of family and friend support, (b) the relative effects of each type of support, and (c) the effects of total support (family and friend support summed). The three models demonstrated partial mediation of adolescents' mental health and self-esteem. Family and total support, but not friend support, partially mediated the relationship between sibling victimization and delinquency. Findings showed that family and friend social support, in combination and sometimes uniquely, reduced the adverse effects sibling victimization associated with adolescents' mental health, self-esteem, and delinquency. Efforts aimed at promoting social support from family and friends as protective factors may reduce the risk of sibling victimization experiences for adolescent well-being difficulties. (PsycInfo Database Record (c) 2020 APA, all rights reserved).