This study evaluated the correlation of residual stenosis after percutaneous transluminal coronary angioplasty with the long-term prognosis. Among consecutive 1,230 patients who underwent coronary angioplasty in the National Cardiovascular Center in Osaka, Japan, 894 patients had de novo lesions. Of these, the 70 patients with acute myocardial infarctions and 105 with unstable angina who had emergency coronary angioplasties were excluded from the study. Among the remaining 719 patients, successful dilatation of the main target vessel was achieved in 592 patients, who then comprised the study group. They were divided into three groups according to their residual stenosis (RS) immediately after coronary angioplasty: group A, RS F 15% (nβ«;)802Ψβ¬ group B, 15% I RS I 35% (n β«Ψβ¬ 286), and group C, 35% F RS F 50% (n β«Ψβ¬ 98). The duration of follow-up was 1,668, 1,660, and 1,680 days in group A, B, and C, respectively. The groups A, B, and C were not significantly different in terms of age, history of myocardial infarction, left ventricular ejection fraction, number of diseased vessels and target vessels, and risk factors such as hypertension, hyperlipidemia, and diabetes mellitus. Primary end point of follow-up was defined as death from any cause and the second end point was occurrence of cardiac events. Kaplan-Meier survival analysis showed significant differences among the three groups. Moreover, survival curves seem to be dependent on the degree of postprocedural residual stenosis. Multivariate analysis using a Cox proportional hazard regression model showed that age, ejection fraction, and residual stenosis were independent determinants of event-free, cardiac, and total survival. Residual stenosis immediately after coronary angioplasty is an independent contributor to long-term clinical prognosis in patients treated with successful balloon coronary angioplasty. Cathet.