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. While most of the endocrinological abnormalities observed in this patient could be attributed to altered endocrine circumstances in CRF, some findings stand in contrast. Furthermore, the testicular biopsy specimen showed severe hypospermatogenesis. Endocrine disorders observed in this patient may be at least in part, responsible for various clinical features underlying WS.