The efficacy of percutaneous transluminal coronary angioplasty (PTCA) in relieving symptoms of coronary artery disease is well established, and the technique has become widely used in patients with multivessel as well as single-vessel disease. The technique has only recently been widely applied, and long-term outcome is, therefore, not well defined. Studies of patients who underwent the procedure early in its development were primarily of patients with single-vessel disease. These studies demonstrated low mortality (1%/yr) and nonfatal myocardial infarction (MI) rates (1-3%/yr), with a majority of patients (85-90%) clinically improved after 5 years. More recent studies of patients with multivessel disease demonstrate higher mortality (2-4%/yr) and a similar incidence of nonfatal MI (2-3%/yr), with improvement in symptoms in the majority (70-80%). The degree of revascularization can be an important factor in symptomatic improvement as well as in the need for subsequent revascularization. A favorable outcome is most likely when all lesions attempted with PTCA are reduced by at least 20% and no significant residual lesions remain in any proximal vessels. The efficacy of PTCA as compared with bypass surgery in patients with multivessel disease is uncertain. The results of several large ongoing and planned clinical trials should provide the information necessary to more fully understand the use of angioplasty in this setting. Although no study has directly compared PTCA with coronary artery bypass surgery, nonrandomized comparisons indicate similar long-term outcomes.(ABSTRACT TRUNCATED AT 250 WORDS)