We studied both the time course and risk factors for adverse clinical events after percutaneous coronary intervention (PCI). Such information is critical to clinical decision-making, but scant quantitative data exist to describe the time course of these adverse outcomes. Patients enrolled in the Integrilin to Minimize Platelet Aggregation and Coronary Thrombosis-II (IMPACT-II) trial were analyzed. Patients undergoing elective, urgent, or emergency PCI (n = 4,010) were randomized to receive either placebo or 1 of 2 eptifibatide regimens during intervention. We evaluated the time to the primary end point of the trial, the 30-day composite of death, myocardial infarction, repeat nonelective PCI, nonelective bypass surgery, or stenting for abrupt closure. Adverse events occurred in 407 patients (10.1%). Because the risk of events declined substantially between 6 and 9 hours (66% occurred within 6 hours), events were classified as occurring before or after 6 hours. Independent predictors of "early" events included dissection, pre- and postprocedural coronary blood flow, side-branch occlusion, procedural thrombolytic use, previous bypass, presentation with unstable angina, absence of diabetes, and hyperlipidemia. The predictors of "late" events included lower weight, increased baseline heart rate, coronary dissection, and procedural thrombolytic use. The risk of ischemic events were greatest immediately after PCI and rapidly declined, so that by 9 hours the hazard function plot was flat; 66% of events occurred within 6 hours of PCI. Knowledge of the risk factors for early and late events help risk-stratify patients before and after intervention for myocardial ischemic events.