Fifty patients who suffered from an acute myocardial infarction at age 40 or below and underwent coronary arteriography, were studied from 8 to 184 months after the infarction (mean follow-up 56 months). Hyperlipidaemia (60%) and cigarette-smoking (82%) were the most common risk factors, while hypertension and diabetes mellitus were found in 10% of all patients. Thirty-seven patients had two or more risk factors. Preinfarction angina was present in 7 subjects. Death rate was 14% within five years and was related to the severity of symptoms. Out of the patients with normal coronary arteriogram (6 patients) or with a single vessel disease 21 were free of angina and 30 did not suffer a reinfarction. Out of 17 patients with two or more coronary vessel disease, angina was present in 14 and reinfarction was seen in 5.