In this study, the authors examined the relationship between engagement in social interaction with peers and stereotypic behavior. Three children with autism with relatively high rates of stereotypic behavior and low rates of social engagement with peers participated in the study. Two typically developing peers learned to direct social initiations to each participant during structured play activities, which increased the frequency of peer social engagement for the children with autism. Collateral decreases in stereotypic behavior occurred for all three participants when the peer-mediated intervention was implemented, and the results generalized to a proximal play setting. Conditional probability analyses further documented this inverse relationship between social and stereotypic behavior. Simultaneous (i.e., motor and oral/vocal) and motor stereotypic behaviors were the most directly affected by the increase in social engagement. Social validity ratings documented the social importance of the changes in both social engagement and stereotypic behavior for the children with autism.