THE TERM "cerebral embolism" has in the course of time acquired a fixed clinical meaning; in its usual connotation this diagnosis portrays an episode of sudden onset, often of rapid fatal termination. This conception of embolic disease of the brain, although deeply rooted in medical thinking, is inadequate. There is mounting indication that often cerebral embolism does not manifest itself as an acute process; this syndrome may, in fact, pursue a subtle, recurrent chronic course ultimately leading to progressive crippling of cerebral function. Cerebral embolism is usually thought of clinically as an acute catastrophic neurological complication occurring in patients with known active cardiac disease. All too familiar is the clinical picture of acute cerebral embolism: A patient with known myocardial infarction, convalescing favorably, is suddenly rendered hemiplegic. However, in some instances the onset of symptoms is insidious and slow. In patients who prove to have cerebral embolism often the cardiac