Abnormal origin of the circumflex coronary artery without any stenosis is generally considered benign and without any particular ischemic risk. We report a case of a 21 year old man who suffered a posterior lateral myocardial infarction with objective criteria: electrocardiographic, echocardiographic and isotopic. The patient received thrombolytic therapy at H2. Angiography showed an abnormal origin of the circumflex coronary artery which was free of any stenosis. Certain cases of the circumflex artery anomaly can, therefore, be complicated by myocardial infarction, and the benign nature of the anomaly needs to be re-examined.