This study compared sibling adjustment and relationships in siblings of children with Autism Spectrum Disorder (ASD-Sibs; n = 69) and siblings of children with typical development (TD-Sibs; n = 93). ASD-Sibs and TD-Sibs demonstrated similar emotional/behavioral adjustment. Older male ASD-Sibs were at increased risk for difficulties. Sibling relationships of ASD-Sibs involved less aggression, less involvement, and more avoidance than those of TD-Sibs. Partial support for a diathesis-stress conceptualization of sibling difficulties was found for ASD-Sibs. For TD-Sibs, broader autism phenotype (BAP) was related to psychosocial difficulties regardless of family stressors. For ASD-Sibs, BAP was related to difficulties only when family stressors were present. This suggests that having a sibling with ASD may be a protective factor that attenuates the negative impact of sibling BAP.