We report a 96-year-old Japanese man who developed a sudden onset of left hemiplegia and coma. He was found to have diabetes mellitus, hypertension, and atrial fibrillation since 1996 with occasional episodes of congestive heart failure. He was otherwise apparently well until July 5 of 1997 when he developed a sudden onset of unresponsiveness and convulsion involving his right hand and was admitted to our hospital. On admission, his BP was 210/120 mmHg, heart rate 76/min and irregular, BT 36.5 degrees C, and Cheyne-Stokes respiration. General medical examination was otherwise unremarkable. Neurologic examination revealed semicoma, conjugated deviation to the right, loss of oculocephalic response, left facial paresis of central type, flaccid left hemiplegia, and bilateral Babinski sign. Pertinent laboratory findings are as follows: BUN 47 mg/dl, creatinine 1.46 mg/dl, GPT 69 IU/l, LDH 1,142 IU/l, and CK 385 IU/l. A chest x-ray film revealed cardiac enlargement and EKG showed left ventricular hypertrophy and atrial fibrillation. Cranial CT scan revealed low density areas involving the right anterior cerebral and the right posterior cerebral artery territories. He was treated with an intravenous osmotic agent and short course of intramuscular steroid. He remained unconscious despite these treatment and developed sudden cardiopulmonary arrest three weeks after the admission. The patient was discussed in a neurological CPC and the chief discussant arrived at the conclusion that the patient had suffered from cerebral embolism of cardiac origin. The cause of the death was ascribed to acute subendocardial myocardial infarction. Most of the participants agreed with this conclusion. Postmortem examination revealed an old subendocardial myocardial infarction involving the posterior septal region and posterolateral wall of the left ventricle. Neuropathologic examination revealed hemorrhagic infarctions involving the territories of the right anterior cerebral, right middle cerebral, right posterior cerebral, and left anterior cerebral arteries. The left A1 portion of the anterior cerebral artery was hypoplastic, and the left pericallosal artery appeared to have been receiving blood supply from the right anterior cerebral artery through the anterior communicating artery. The large arteries in the base showed marked arteriosclerosis; particularly, the initial portion of the right posterior artery showed near complete arteriosclerotic occlusions. These characteristic arterial changes appeared to be the reason why this patient suffered from an extensive infarction from what appeared to have been a single episode of cerebral embolism probably initially involving the right internal carotid artery.