The object of this study of 30 patients with an anomalous origin of the left circumflex coronary artery was to define the clinical and angiographic features of this condition and to assess its influence on morbidity and survival. The 30 patients were 24 men and 6 women with ages ranging from 29 to 76 years. An anomalous origin of the left circumflex coronary artery should be suspected when two angiographic signs are present: firstly, the visualisation of a spur of opacification in the 30 degrees LAO view of left ventriculography, present in 93% or our patients; secondly, during selective left coronary angiography in the transverse view, an ascular zone is observed where the normal left circumflex artery should be. Confirmation of the diagnosis depends on opacification of the left circumflex arising from the right anterior sinus of Valsalva with a separate (37%) or common (23%) orifice with the right coronary artery or arising from a proximal segment of the right coronary artery/(40%). Five patients (17%) had a significant stenosis of the anomalous left circumflex coronary artery but this was always associated with lesions of the other coronary narrowing was observed. Of these patients, one had electrocardiographic signs of myocardial ischaemia and no other cause apart from the anomalous origin of the left circumflex to explain this ischaemia. The 30 patients were followed up for an average of 6.1 +/- 3.9 years. During this period, 1 cardiac death, 1 infarction, 5 cases of angina, 4 coronary bypass procedures, and 6 coronary angioplasties were observed. Nine patients (30%) had no cardiac event during follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)