Research on the experiences of siblings of individuals with ASD and the quality of their sibling relationships has yielded mixed results. The present study examined the significance of parent- versus child-report of both positive and negative behaviors exhibited by siblings and their brothers and sisters with ASD within sibling dyads. Findings indicated that siblings were more positive in their assessment of the sibling relationship than were their parents. Siblings exhibited more positive behaviors within the sibling relationship than did their brothers and sisters with ASD, and were recipients of aggression. These findings are consistent with prior research suggesting that siblings tend to take on a caretaking role, and point to important targets for intervention.