In order to evaluate the medical, psychological and behavioral aspects of Williams-Beuren syndrome in adulthood, data were collected on 11 patients aged 17 to 66 years. The medical data did not confirm previous reports of significant morbidity. All adults were found to have a moderate or severe degree of mental handicap. They showed the same psychological profile as found in children: good verbal abilities, poor motor abilities, problems with sequencing and with performance tasks. The adults we evaluated showed little disturbing behavior in comparison to other mentally retarded subjects. They achieved a good level of autonomy. The majority lived at home with one or both parents and attended a day centre.