A 58-year-old woman, with a past history of classic migraine since youth, suddenly experienced blurred vision and flexor spasms of her left hand, followed by a right hemicrania and photophobia, similar to previous attacks of migraine. Within a few hours a progressive left hemiplegia and paralysis of left conjugate gaze developed. Severe right hemicrania continued. CT brain scans showed a progressing large right parietotemporal infarct. Her level of consciousness declined and she died ten days after admission to hospital. The autopsy showed a large infarct in the area of supply of the right middle cerebral artery, associated with oedema and with a shift of midline structures to the left, with cingulate and right hippocampal herniation. There was secondary midbrain haemorrhage. Recent secondary haemorrhagic infarction was present in the left calcarine cortex. The carotid arteries in the neck showed only minimal atheromatous change and were patent; the cerebral arteries were remarkably free of atheroma, but the right middle cerebral artery contained red thrombus. Histologically the cerebral infarction antedated the middle cerebral artery thrombus by several days, supporting arterial spasm as the cause of infarction. The thrombosis was considered to be a secondary phenomenon.