Background: Although the protective effects of familial and parental support have been studied extensively in the child psychopathology literature, few studies have explored the protective quality of positive sibling relationships. Methods: A two-wave longitudinal design was used to examine the protective effect of positive sibling relationships on child adjustment for children experiencing stressful life events. Mothers reported on stressful life events and child adjustment. Older siblings assessed the quality of relationship between themselves and target children. Results: Sibling affection moderated the relationship between stressful life events and internalizing symptomatology but not the relationship between stressful life events and externalizing symptomatology. Notably, the protective effect of sibling affection was evident regardless of mother-child relationship quality. Conclusions: Positive sibling relationships are an important source of support for children experiencing stressful life events. Implications for intervention are discussed.