In this article, we review the literature on siblings of individuals with autism spectrum disorders (ASD) from a lifespan developmental perspective, from infancy through adulthood, focusing on the sibling relationship and sibling well-being. We situate this review within the larger body of research on siblings of individuals with developmental disabilities (DD) across the lifespan. We then consider the genetic aspects of ASDs and their implications for siblings. We conclude that there is an evidence of atypical social and communication development in some siblings of children with an ASD during infancy. During childhood and adolescence, siblings describe both positive and negative aspects of their sibling relationship and there is some evidence that siblings of children with an ASD may be at heightened risk for social and behavioral adjustment problems. The limited research on adulthood suggests that lack of closeness in the sibling relationship and social and emotional difficulties may continue. We encourage more attention focused on developmental issues, specifically with respect to samples in narrower age groups and in longitudinal research. Finally, we note the variability in sibling outcomes, and suggest further examination of potential moderating and mediating factors, including genetic predispositions. © 2007 Wiley-Liss, Inc. MRDD Research Reviews 2007;13:313–320.