To investigate the effect of diabetes on stroke after myocardial infarction (MI), we studied consecutive MI patients admitted to the coronary-care unit prospectively, and compared diabetics with non-diabetics. Seven per cent (11/148) of diabetics and 3% (8/297) of non-diabetics had a stroke within 1 month after MI (P = 0.020). Previous stroke and hypertension were significant risk factors for stroke after MI in diabetics, but there were no significant risk factors in non-diabetics. Hypertension was more frequent in diabetics with (12/14; 86%) than in diabetics without (63/134; 47%) a previous stroke (P less than 0.025). Severe hypotension was more frequent in diabetics (9/11) than in non-diabetics with stroke after MI (0/8) (P = 0.002). We conclude that hypertension is a risk factor for stroke after MI in diabetics, and that may be at risk for hypotensive stroke after MI. Stroke after MI may be more frequent in diabetics than in non-diabetics.