Introduction：Hyponatremia, which is frequently present in patients with end-stage cancer, causes delirium and disturbance of consciousness and is considered a poor prognostic factor. We report a case of hyponatremia with hypopituitarism in association with leptomeningeal metastasis, resulting in reversible disturbance of consciousness. Case report：A 77 year-old female received chemotherapy at our hospital for postoperative recurrence of lung cancer, and best supportive care due to a side effect. After transfer to another hospital, she experienced a sudden disturbance of consciousness and was returned to our hospital. A detailed examination resulted in a diagnosis of hyponatremia from hypopituitarism following leptomeningeal metastasis involving the cerebral ventricles. Hyponatremia was improved by NaCl supplement and hormone replacement, followed by recovery from disturbance of consciousness. Discussion：QOL of patients with end-stage cancer can be improved through the active treatment of reversible causes of disturbance of consciousness. Conclusion：When severe hyponatremia is detected in cancer patients, it is important to consider the possibility of hypopituitarism with brain metastasis or meninges dissemination in the differential diagnosis.