We used a computer data bank to evaluate 740 consecutive patients admitted to a cardiac care unit with myocardial infarction. Stroke occurred in 18 (2.4%) patients in the hospital; the anterior circulation was involved in 76% of strokes. Hospital mortality was 61% in patients with stroke and 13% in patients without stroke. Atrial arrhythmia was a significant (p less than or equal to 0.03) risk factor for stroke, but peak creatine kinase and ventricular arrhythmia were not. Cardiac pump failure, apical or anterior-lateral myocardial infarction, and history of previous stroke were associated with an increased risk of stroke. Clinical and pathologic data suggested an embolic etiology for most strokes that complicate acute myocardial infarction.