Hyponatremia is one of the major side effects that occurs after CDDP-based cancer chemotherapy. However, RSWS has rarely been reported as a cause of hyponatremia occurring after chemotherapy containing CDDP. A 70-year-old female who had recurrent lung adenocarcinoma after surgery was treated with CDDP, pemetrexed and bevacizumab-containing chemotherapy. She suffered from acute-onset consciousness disturbance and hyponatremia on day 3 of chemotherapy. Although SIADH was considered at the time of onset, the patient was subsequently diagnosed with RSWS, based on observations of dehydration, high levels of urinary sodium excretion and evidence of renal tubule failure. She recovered from these conditions without any residual disability after infusion of hypertonic saline fluid on day 13 of chemotherapy. In this report, we have described RSWS, which is rare complication that may follow CDDP-based chemotherapy. It is important, but not very easy, to distinguish between SIADH and RSWS clinically for the selection of an appropriate treatment.