The hospital mortality of acute myocardial infarction amongst 285 known diabetics treated in the last decade was 39.7 per cent at one month and had increased to 51 per cent at 12 months. Treatment in a coronary care unit during the acute stage had little effect on the mortality amongst patients on insulin, but was beneficial for patients whose diabetes had been controlled by oral hypoglycaemic drugs. Female patients on oral hypoglycaemic drugs had the highest mortality. When considering age, duration of diabetes and presence of retinopathy, acute myocardial infarction in diabetics controlled on oral therapy appeared to have a worse outcome than in patients on insulin. Independently of whether patients were on insulin or on oral hypoglycaemic drugs 12 months after the acute episode, only about half of them were still alive.