Authors report two cases of myocardial infarction occurred before the age of twenty: the former in a man without risk factors, who had 12 years later a cerebral embolic stroke, caused by a left-ventricular thrombus; the latter in a young woman who was taking oral contraceptives. The review of the literature shows that the prevalence of myocardial infarction in juvenile age is not negligible. Especially in those cases occurred before the age of 35, risk factors, clinical features, coronary angiographic findings and possible pathogenetic mechanisms are quite different from those generally observed in elderly patients. Cigarette smoking and estro-progestinic drugs represent the main risk factors; myocardial infarction is often the first event of ischaemic heart disease and usually effort angina is lacking; several patients have patent coronary arteries or minor (single vessel) lesions and collaterals are generally absent; coronary spasm and/or intravascular thrombosis probably play a predominant pathogenetic role.