Siblings of children with developmental disabilities were assessed twice, 2 years apart (N = 75 at Time 1, N = 56 at Time 2). Behavioral adjustment of the siblings and their brother or sister with developmental disability was assessed. Comparisons of adjustment for siblings of children with autism, Down syndrome, and mixed etiology mental retardation failed to identify group differences. Regression analysis showed that the behavior problems of the child with developmental disability at Time 1, but not the change in their behavior over time, predicted sibling adjustment over 2 years. There was no evidence that this putative temporal relationship operated bidirectionally: sibling adjustment did not appear to be related to the behavior problems of the children with developmental disabilities over time.