Williams syndrome (WS) is a neurodevelopmental disorder caused by a deletion in the 7q11.23 region which includes at least 17 genes. The presence of autistic features in WS is a controversial issue. While some authors describe WS as the opposite phenotype of autism, recent studies indicate that both share many common characteristics. We report a 12-year-old boy diagnosed as autistic disorder and WS with hemizygosity at the elastin locus and a karyotype of 46,XY,del(7)(q11.21q11.23). Molecular genetic studies have shown that deletion at the elastin gene may account for the cardiovascular abnormalities seen in WS, but autistic features are likely caused by other genes flanking elastin.