Seventy-five patients with greater than or equal to 70% stenosis of the left main coronary artery (LMCA) were treated surgically between January 1974 and February 1980. The group consisted of 57 men and 18 women with a mean age of 62.8 years. All patients were symptomatic with angina pectoris, and 64 (85%) had unstable angina. Twenty-nine patients (38.6%) had electrocardiographic evidence (ECG) of old myocardial infarction (MI) and only six (8%) had a normal resting ECG. Preoperative exercise testing was done in 22 of the 75 patients. The stress test was positive in all patients, 17 (77%) of whom had greater than 2 mm ST depression; 90.6% (68/75) had significant right coronary artery disease. The intra-aortic balloon pump (IABP) was inserted preoperatively in only four patients (5%) and was required in two additional patients postoperatively. The IABP was inserted preoperatively in four patients because of medically refractory angina and not on the basis of coronary anatomy alone. An average of three grafts per patient were inserted. There were three (4%) postoperative myocardial infarctions and two (2.6%) deaths. During the follow-up period, which comprised 105 patient-years, there was one myocardial infarction and one death. These data indicate that successful surgical treatment of left main coronary artery disease can be achieved with low mortality and that routine preoperative insertion of IABP is unnecessary.