A 12-year-old girl with short stature due to idiopathic Fanconi syndrome and chronic renal failure was treated with recombinant human growth hormone (rhGH). There was no family history of diabetes mellitus and the glucose tolerance before treatment was normal. Intravenous glucose tolerance tests were performed before, during and after treatment. Two months after starting rhGH the early phase of insulin secretion (1-+3-min values) was diminished, and the patient developed manifest diabetes mellitus with hyperglycemia and an elevated hemoglobin A1c. Following discontinuation of rhGH, glucose tolerance slowly returned to normal.