A 31-year-old man who had been under regular hemodialysis for 6 months was diagnosed as Williams syndrome (WS) by fluorescence in situ hybridization (FISH) chromosomal analysis. The association of WS and chronic renal failure (CRF) is only rarely encountered. Endocrinological examinations revealed hypergonadotropic hypogonadism. Prolonged and exaggerated responses of adrenocorticotropin (ACTH) to insulin-induced hypoglycemia and corticotropin releasing hormone (CRH) were also noted.