Coronary arteriography was performed in 50 patients aged 40 years of less all of whom had had acute myocardial infarction (AMI). Forty-seven patients had at least one risk factor for development of ischaemic cardiac disease. Smoking and familial predisposition were the commonest predisposing factors. Seventeen patients had stenosis in a single coronary artery only. Six patients had three-vessel disease and none had stenosis of the main stem of the left coronary artery. Eight patients had no stenoses. All patients with three-vessel disease had sign of ischaemia after infarction. The type of infarction was related to the number of stenosed vessels, so that patients with Q-wave infarction had a greater number of stenoses than patients with non-Q-wave infarcts. A congenital coronary in the form of abnormal origin of the left coronary artery from the pulmonary artery was the cause of AMI in an isolated case. On the basis of this retrospective investigation, the authors have assessed the value of routine coronary arteriography (CAG) in 50 relatively young patients who had recently sustained AMI. CAG does not appear to be indicated as a routine procedure in all of these patients but could have been performed primarily on the basis of symptoms or the findings from non-invasive investigations.