To identify risk factors for restenosis, we evaluated data in 473 patients with single-vessel percutaneous transluminal coronary angioplasty (PTCA) and control angiography after 6 months. Restenosis, defined as (1) loss greater than 50% of the initial gain, and (2) stenosis greater than 50% was found in 138 patients (29.2%). Univariate analysis revealed eight factors related to restenosis: (1) duration of symptoms less than 1 month (P = 0.005), (2) unstable angina (P = 0.004), (3) high-grade stenosis before PTCA (P = 0.014), (4) large residual stenosis after PTCA (P = 0.001), (5) insufficient improvement of stenosis (P = 0.042), (6) prolonged single inflation time (P = 0.017), (7) prolonged total inflation time (P = 0.055), and (8) low inflation pressure (P = 0.028). Multivariate analysis revealed four factors significantly related to restenosis: (1) large residual stenosis after PTCA (P = 0.0001), (2) prolonged single inflation time (P = 0.0047), (3) unstable angina (P = 0.0127), and (4) high-grade stenosis before PTCA (P = 0.0179). Modification of procedural factors might be helpful to reduce the risk of restenosis after successful PTCA.