Existing research studies have shown mixed results relating to the impact upon children of having a sibling with a disability. However, siblings of children with autism may be more at risk than siblings of children with other disabilities. In the present study, data were gathered on 22 siblings of children with autism. These children were rated by their mothers as having more behavior problems and fewer prosocial behaviors than a normative sample. Analysis of variables predicting sibling behavioral adjustment revealed that boys with siblings who have autism, and also those younger than their sibling with autism, engaged in fewer prosocial behaviors. Psychological adjustment of mothers (stress) and the child with autism (behavior problems) were not predictive of sibling behavioral adjustment.