An autopsy case of secondary diabetes insipidus associated with subarachnoideal hemorrage, which had been considered a rare cause of diabetes insipidus, was reported. The patient was a 54-year-old male who was admitted to our hospital on April 17, 1978 with the chief complaints of severe headache and vomitting. He had hypertension for 10 years. Two weeks prior to admission he experienced transient headache. In the morning of April 12, 1978 he developed severe headache associated with vomitting after defecation. His headache was containued until the time of admission. On physical examination the patient was awake and alert. General physical examinations were unremarkable except for high blood pressure (156/90 mmHg) and mild nuchal rigidity. Fundoscopic examination revealed the hypertensive changes (KW IIa). The lumbar puncture revealed that the opening pressure was 220 mmH2O, and the CSF was bloody. One and a half hours after admission, patient became deeply comatous suddenly, and the pupils became dilated and fixed to light. And occasionaly apnea was noted; therefore, dexamethazone was administered and oxygen inhalation was started. However, the apnea continued and the patient was placed on the respirator. Thereafter, polyuria developed; the urine volume was 600 to 1340 ml/hr with the specific gravity of 1.0041.006. Following the administration of vasopressin, the urine volume decreased and the specific gravity of the urine increased. However, the patient did not recover and expired 43 hours after the admission. Postmortem examinations revealed subarachnoideal hemorrage due to the rupture of the aneurysm of the left anterior communicating artery, which penetrated to the ventricular system. Histological findings revealed that the hypothalamus was necrotic; especially, the supraoptic and paraventricular nucleus were disappeared, and the anterior and posterior lobe of the pituitary were also necrotic.