A 61-year-old woman was admitted to our hospital because of hoarseness and abnormal shadow on chest X-ray. We diagnosed this patient as large cell carcinoma of the right upper lobe of the lung; T3N3M1 Stage IV. She was treated with OK-432, CDDP and CQ. On the 6th day after 2nd cycle chemotherapy, she was confused, and we diagnosed her as a case of hyperosmolar nonketotic coma (HNC) on the 7th day. Unfortunately, she died on the 8th day, after 20 hours of treatment for HNC. She suffered from chronic dehydration due to trouble with left recurrent nerve palsy. Although continuous intravenous hyperalimentation was used, she had severe HNC. HNC might be one complication in chemotherapy for patients with malignancy.