One hundred thirty-eight men aged less than or equal to 39 years had coronary bypass grafting during a 13 year period. Angina was the presenting symptom in 77% and of these patients, one-third had unstable angina. More than half of the patients had experienced at least one myocardial infarct. There was a high incidence of coronary risk factors, especially smoking. Nineteen patients (13.8%) had left main coronary artery stenosis (it was isolated in two); 13.8, 24.6 and 60.2% had single, double and triple vessel disease, respectively. Left ventriculograms showed serious functional impairment in 42%. A total of 461 coronary bypass grafts, 3.34 per patient, were placed; almost all were vein grafts. There were no operative deaths. Transmural myocardial infarction occurred in 4.3% of patients. All bypass grafts were opacified angiographically early after operation, 95% at 1 year, 56% at 5 years and 26% at 10 years after operation. Some patients also had coronary angiograms, dictated by clinical events, between 1 and 5 and between 5 and 10 years postoperatively. Patency rates for bypass grafts were comparable with those previously reported and were acceptable, although they decreased with time. However, increasing evidence of atherosclerosis of bypass grafts was seen beyond 1 year, particularly beyond 5 years. Of 23 subjects with a coronary bypass reoperation, 2 died and 44% had perioperative transmural myocardial infarction. During follow-up, 13.8% of the patients died, survival being 95, 84 and 76% at 5, 10 and 12 years, respectively. It is considered that the patients were advantageously treated with coronary bypass grafting especially in the short-term. However, bypass graft patency steadily decreased with the passage of time and graft atherosclerosis became an increasingly important problem.