Significant left main coronary artery disease is a separate disease entity in coronary artery disease. The prognosis is classically poor and the treatment of choice is surgical. A retrospective study of patients with left main coronary disease, diagnosed and treated at the CHRU Dupuytren, Limoges, between 1/01/80 and 15/06/91 was undertaken to determine the aetiological, clinical and therapeutic factors which influence mortality related to this condition. During this period, 8198 coronary angiographies were performed in the cardiology department. The diagnosis of significant left main coronary disease (> or = 50% stenosis) was made in 250 cases (3% of all investigations). Of these 250 cases, 227 were treated medically or surgically by our group during the study period. Twenty patients were treated in another centre and 3 underwent surgery after the 15/06/91. Seven patients died in the period immediately after coronary angiography. Of the 220 survivors of coronary angiography, 185 (85%) were referred for surgery (direct or sequential venous and/or arterial bypass or coronary endarteriectomy). Four patients died within 30 days of surgery. Thirty five patients were treated medically. The therapeutic decision was based on the absence of surgical contra-indications. The retrospective, non-randomized nature of this study with allocation of patients to surgical or medical treatment without control invalidated statistical analysis. At the date of the last follow-up appointment, arbitrarily chosen as the 1/01/93, 163 operated patients (88.1%) of which 130 (79.7%) were asymptomatic and 13 medically treated patients (37%) were alive. The prognostic factors after surgery in this study were: stage IV dyspnoea at the time of diagnosis, severe abnormalities on catheter study (end diastolic pressure over 18 mmHg after angiography), left ventricular wall abnormalities (functional score > 10) and incomplete revascularization. The risk of coronary angiography in this condition were confirmed in this study.