BACKGROUND: Children's exposure to parental violence against another parent has been widely studied as an adverse childhood experience and source of childhood trauma. Exposure to parental violence against a sibling could be equally as traumatizing, but the literature on this exposure is sparse, by comparison. We examined the frequency of exposure to parental assault on a sibling (EPAS) and its demographic distributions. We also investigated the links between EPAS and symptoms of distress. METHOD: From three combined surveys of the National Survey on Children's Exposure to Violence, based on telephone interviews with parents, and in the case of those 10-17 years old, adolescents, we examined children living with a juvenile sibling (N = 7, 029; 49% female). RESULTS: Lifetime EPAS was 3.7%, and sibling assault was more common by fathers (70%) than by mothers (30%). Exposure was greatest for boys and adolescents, highest for those whose parents had some college education, and for those living with other non-parental adults, single parents, and stepfamilies. Rates did not differ by ethnicity. Most exposed youth felt afraid (83%), and fear was greater when witnessing fathers than mothers assaulting a sibling. Controlling for child maltreatment and exposure to interparental violence, those exposed to EPAS showed higher current levels of mental distress (anger, depression, and anxiety; F (10, 6146) = 140.44, p = .001; R2 = 0.19). CONCLUSIONS: Clinical work and parent education programs should address the occurrence of EPAS and the adverse association between EPAS and mental health to reduce its potential negative impact.