Objectives The aim of this study was to test the noninferiority of eptifibatide relative to abciximab in patients with ST-segment elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI). Background Glycoprotein IIb/IIIa inhibitors are recommended by international guidelines in patients with acute coronary syndromes undergoing PCI. Abciximab is recommended with a higher level of evidence than eptifibatide in patients with STEMI. No large, prospective, randomized trial comparing abciximab and eptifibatide has been published. Methods All (n = 11,479) STEMI patients in Sweden who underwent primary PCI and received either eptifibatide or abciximab from 2004 to 2007 were derived from the SCAAR ( Swedish Coronary Angiography and Angioplasty Registry). The primary end point was death or myocardial infarction (MI) during 1-year follow-up, with adjustment for baseline differences with a multivariate logistic regression analysis including propensity score. The pre-specified noninferiority margin was set to 1.29. Results The combined end point occurred in 353 of 2,355 patients (15.0%) treated with eptifibatide and in 1,432 of 9,124 patients (15.7%) treated with abciximab. The unadjusted odds ratio ( OR) for eptifibatide versus abciximab was 0.95 (95% confidence interval [CI]: 0.84 to 1.08). Multivariate adjustment (n = 11,317) confirmed noninferiority, with an OR of 0.94 ( 95% CI: 0.82 to 1.09). The adjusted secondary end points of death and MI separately also showed noninferiority, with ORs of 0.99 ( 95% CI: 0.82 to 1.19) and 0.88 ( 95% CI: 0.73 to 1.05), respectively. Conclusions This large registry study suggests that eptifibatide is noninferior to abciximab in patients with STEMI undergoing primary PCI with respect to death or MI during 1 year, thereby supporting the use of either drug in clinical practice.