The report was made on congenital nephrogenic diabetes insipidus which was observed in an 11-year-old boy. 1. IVP demonstrated hydronephroureter and enlarged bladder. 2. The obstruction of urethra and VUR were not discovered by UCG and there was no residual urine. In the cystoscopic examination, the trigone and bilateral ureteral olifice were normal, and cystometrogram demonstrated almost normal pattern of the bladder function. 3. After the open renal biopsy, polyuria appeared because of, may be, both the absense of thiazide effect and the diabetic diuresis. But, urine volume decreased in several hours as the result of the postoperative administration of thiazide. 4. In this case, the decrease of urine volume could be observed probably as the result of the administration of thiazide even in hypernatremic state.