Parents' attributions of the jigsaw-puzzle performance of their child with Prader-Willi syndrome (n = 20) or Williams syndrome (n = 21) were examined. Parents in both groups placed more importance on internal versus external attributions. Parents of children with Prader-Willi syndrome exhibited a hedonic bias by attributing their child's success to internal factors (particularly when the child was good at puzzles), downplayed the role of chance when their child had higher puzzle skills and higher cognitive functioning, and differentiated between internal and external attributions. In contrast, parents of children with Williams syndrome showed an inconsistent attributional pattern. These findings help identify how parents understand the intellectual performance of their child with disabilities and how interventions might be beneficial.