ABSTRACT
We describe a case of congenital nephrogenic diabetes insipidus with severe dilatation of bilateral urinary tracts without anatomical obstructions. Functional obstruction can be occurred when polyuria surpasses the transporting ability of urine in the urinary tract. The patient was admitted to our hospital due to decreased mentality developed after traffic accident. On radiologic study, bilateral hydronephrosis and hydroureter were noted. Because the patient excreted copious dilute urine, we performed water deprivation test and the result was consistent with nephrogenic diabetes insipidus. We are presenting this case in an attempt to describe strong association between congenital diabetes insipidus and nonobstructive hydronephrosis in which polyuria is responsible for the hydronephrosis.