Objectives. The purpose of this study was to evaluate the incidence and predictors of early (<30days) stent thrombosis (ST) in pts with acute coronary syndromes (ACS) in the drug-eluting stent (DES) era. Background. Predictors of ST, including detailed quantitative coronary angiographic (QCA) analysis parameters have not been carefully investigated in pts with ACS. Methods. In the prospective, multicenter ACUITY trial, a total of 7,179 pts with moderate and high risk ACS were treated with stents (66.4% of whom received at least 1 DES). Among these pts, core lab QCA was performed in 3,518 (49.0%) pts. Results. Within 30 days, 101 pts (1.4%) suffered definite or probable ST by the Academic Research Consortium (ARC) definition. Pts with ST were older and had a higher prevalence of diabetes mellitus, prior MI and renal insufficiency, higher TIMI risk scores and ST segment deviation compared to those without ST. By core lab QCA pts with ST were more likely to have greater overall coronary artery disease burden, procedural angiographic complications, suboptimal final angiographic results, implantation of ≥2 stents, and use of aspirin <50% of time within 30 days. A final stent diameter stenosis >20% and implantation of ≥2 stents were the strongest independent predictors of early ST (Table ). DES use was not significantly different between pts with and without ST (62.4% vs. 66.5%, P=0.40). Conclusions. Early ST in pts with ACS is frequent with both BMS and DES, and is predicted by use of multiple stents and suboptimal angiographic results. Avoiding multiple stents and improving operator technique and antiplatelet compliance may minimize the risk of early ST in ACS. Multivariate predictors of early ST