Williams syndrome (WS) is a genetic disorder caused by the hemizygous microdeletion in chromosome 7q11.23. It is characterized by dysmorphic face, cardiovascular disease, idiopathic hypercalcemia, mental retardation, and an uneven profile of cognitive-linguistic abilities and deficits. The presence of autistic features in individuals with WS is a controversial issue. While there are reports that describe them as overly friendly with excessive sociability and good empathic skills, some recent studies focus more on the qualitative impairment of their social abilities. Here, we report the clinical presentation and follow-up of an eight-year-old boy with WS and clear problems in his social interaction, non-verbal communication and circumscribed interests. To our knowledge, this is the first case report on the coexistence of WS and Asperger's disorder. It also differs from previous papers on the comorbidity of WS and autism spectrum disorders, by depicting a highly verbal, nonretarded child followed for seven years through adolescence.