ABSTRACTTo determine risk factors for restenosis, we studied 998 patients who underwent elective coronary angioplasty (PTCA) to native coronary arteries between July 1980 and July 1984. Restenosis, defined as a luminal narrowing of greater than 50% at follow-up, was present in 302 patients (30.2%). Univariate analysis of 29 factors revealed seven factors related to restenosis: vessel dilated (circumflex coronary artery 18%, right coronary artery 27%, left anterior descending artery 34%; p <.01), final gradient of 15 mm Hg or less compared with greater than 15 mm Hg (27% vs 38%, p <.01), duration of angina greater than 2 months compared with angina of shorter duration (27% vs 35%, p = .01), post-PTCA stenosis of 30% or less compared with 31% to 50% (28% vs 36%, p <.025), stable vs unstable angina (26% vs 34%, p <.05), presence vs absence of intimal dissection (26% vs 32%, p = .07), and female gender vs male gender (25% vs 32%, p = .08). Multivariate analysis revealed five factors independently related to increased risk of restenosis in the following order of importance: PTCA in the left anterior descending artery, absence of intimal dissection immediately after PTCA, final gradient greater than 15 mm Hg, a large residual stenosis after PTCA, and unstable angina. Restenosis after PTCA is a multifactorial problem. The hemodynamic and angiographic result at the time of PTCA significantly influences long-term outcome, but additional measures aimed at reducing the rate of recurrence of atherosclerotic plaque are required.