Using univariate and multivariate analyses, we evaluated the relation between ischemic and bleeding complications and peak procedural activated clotting time (ACT) in patients undergoing percutaneous coronary intervention whose coronary narrowings were treated with stent implantation. Of the 2,280 patients who qualified for the study, 29% had diabetes mellitus, and 91% received glycoprotein IIb/IIIa inhibitors. The median for ACT was 276 seconds (interquartile range 243 to 317). The incidence of ischemic events by ACT quartiles was 6.3%, 7.5%, 8.1%, and 7.1%, respectively (p=0.71). The incidence of bleeding complications was 6.6%, 5.9%, 6.9%, and 7.3%, respectively (p=0.81). ACT did not independently predict either ischemic or hemorrhagic complications.