Two hundred patients (mean age 56 years, range 36 to 74) with unstable angina (chest pain at rest, associated with ST-T changes) underwent coronary angioplasty. In 65 patients with multivessel disease, only the "culprit" lesion was dilated. The initial success rate was 89.5% (179 of 200 patients). At least one major procedure-related complication occurred in 21 patients (10.5%): (death in 1, myocardial infarction in 16 and urgent surgery in 18). All patients were followed up for 2 years. Five patients died late; 8 had a late nonfatal myocardial infarction and 52 had recurrence of angina pectoris. The restenosis rate was 32% (51 of 158) in the patients with initial successful angioplasty who had repeat angiography. At the 2 year follow-up, after attempted coronary angioplasty in all 200 patients, the total incidence rate of death was 3% (one procedure related; five late deaths), of nonfatal myocardial infarction 12% (16 procedure related and 8 late after angioplasty), and 13% (26 patients) were still symptomatic although they had improved in functional class. Multivariate analysis showed that variables indicating an increased risk 1) for major procedure-related complications were: ST segment elevation, persistent negative T wave and stenosis greater than or equal to 65% (odds ratio 3.7, 3.7 and 3.3, respectively); 2) for angiographic restenosis were: presence of collateral vessels, ST segment depression, multivessel disease, left anterior descending coronary artery stenosis and history of recent onset of symptoms (odds ratio: 2.2, 2.0, 1.9, 1.9 and 0.54, respectively); and 3) for late coronary events (recurrence of angina, late myocardial infarction or late death) were: multivessel disease, total occluded vessel and ST segment elevation (odds ratio 3.7, 2.8 and 0.44, respectively). Thus, coronary angioplasty for unstable angina can be performed with a high initial success rate, but at an increased risk of major complications. The prognosis is favorable after initial successful coronary angioplasty.