Myocardial infarction is an uncommon event in childhood and adolescence, and only rarely is found to be due to atherosclerotic disease. This report describes a 15-year-old diabetic female with an acute anterior wall myocardial infarction in whom initial coronary angiography showed a thrombus of the proximal anterior descending coronary artery which had resolved spontaneously by the time a follow-up study was carried out six weeks later. None of the usual precipitating causes of myocardial infarction in childhood were found, and repeat angiography did not demonstrate any fixed coronary artery disease. The relevant literature is reviewed and it is speculated that endothelial dysfunction, coronary spasm and altered coagulability may have contributed to the formation of intraluminal thrombus and subsequent infarction in this patient.