Acute coronary events reported in patients enrolled in the NHLBI PTCA Registry were analyzed. Data were collected on 3,079 patients from 105 contributing centers. Coronary vascular events (dissection, occlusion, spasm, embolism, perforation or rupture) or ischemic events (MI or prolonged angina) occurred in 418 patients (13.6%). Major complications (MI), emergency surgery or death) occurred in 280 patients (67%) with acute coronary events. The most frequent events were prolonged angina, which occurred in 211 (6.8%), and MI, in 170 (5.5%). Coronary dissection, occlusion and spasm each occurred in approximately 5% of patients. Coronary embolism, perforation and rupture were rare (less than 0.2% for each). Dissection and occlusion each had a high frequency (greater than 80%) of associated major complications. A substantially lower incidence of major complications occurred in patients with isolated coronary spasm (18%) or prolonged angina (35%). Clinical and angiographic predictors for overall and specific events were identified. Coronary events occurred more frequently in women and patients with unstable angina. Eccentric lesions were associated with a higher rate of coronary events, and event rates were lower with single discrete lesions than with other types of lesions. The frequency of any coronary event, MI, prolonged angina and coronary spasm each decreased with increasing experience with PTCA. The frequency of dissection and occlusion did not change with experience.