A 69-year-old woman diagnosed with a urinary carcinoma was admitted to the hospital for chemotherapy consisting of cisplatin (CDDP) and gemcitabine. Two days after administration of CDDP, she complained of general fatigue. The total urine volume was 5, 500 ml/day. Three days after she received CDDP, her serum sodium level decreased to 118 mEq/l, leading to disturbed consciousness. After the intravenous administration of saline, her serum sodium levels recovered to the normal value (137 mEq/l) without any complications. The diagnosis of renal salt-wasting syndrome was made on the basis of hyponatremia, high urinary sodium excretion and increased urinary output.