In the present study, the authors investigated the effectiveness of a sibling-mediated intervention in supporting the social behaviors of young children with autism. They used a multiple-baseline design across four sibling dyads to examine the effectiveness of the intervention. The researchers taught the typically developing siblings ways to socially engage their brothers with autism, which resulted in strong and positive changes in joint attention and modest changes in social behavior for the latter. Social validity ratings by observers who were naive to the study parameters documented the social importance of the intervention effects for three of the four children; however, the results did not provide strong evidence for generalization of increased social interactions to different settings. The authors also discuss the practical implications of their findings.