Coronary artery bypass grafting (CABG) and percutaneous transluminal coronary angioplasty (PTCA) are more effective than medical treatment for the management of ischaemic heart disease. However, patients with single-vessel involvement have been excluded from prospective comparisons of the two methods. We have carried out such a comparison in patients with isolated proximal left anterior descending artery stenosis, conserved left ventricular function, and documented ischaemia. Eligible patients presenting to a single centre were randomly assigned PTCA (68 patients) or left internal mammary grafting (66). The procedures were technically feasible in all cases. The incidence of in-hospital complications was 2% (perioperative myocardial infarction) for CABG and 3% (emergency CABG for acute closure) for PTCA. Clinical and functional status improved similarly in both groups. However, patients in the PTCA group took more antianginal drugs. At median follow-up of 2.5 years, 86% of CABG-treated and 43% of PTCA-treated patients were free from adverse events (p < 0.01; relative risk 2.0 [95% CI 1.7-2.3]). The adverse events that explain this difference were restenosis (32%) requiring subsequent surgical (16%) or percutaneous (15%) revascularisation (1% had medical therapy). Rates of cardiac death and myocardial infarction did not differ between the groups. Both CABG and PTCA improve the clinical status of symptomatic patients with single-vessel coronary artery disease. If patient and physician accept the risk of restenosis and reintervention associated with PTCA, this procedure remains a suitable option and a simpler initial alternative to CABG.