Background Diabetic patients are at increased risk for future cardiovascular events after ST-segment elevation myocardial infarction (STEMI). Administration of an intracoronary abciximab bolus during primary percutaneous coronary intervention (PCI) may be beneficial in this high-risk subgroup. Objectives This study sought to report the 1-year clinical outcomes and cardiac magnetic resonance (CMR) findings in STEMI patients with and without diabetes randomized to intracoronary or intravenous abciximab bolus at the time of primary PCI. Methods Patient-level data from 3 randomized trials were pooled. The primary endpoint was the composite of death or reinfarction. Comprehensive CMR imaging was performed in 1 study. Results Of 2,470 patients, 473 (19%) had diabetes and 1,997 (81%) did not. At 1 year, the primary endpoint was significantly reduced in diabetic patients randomized to intracoronary abciximab compared with those randomized to intravenous bolus (9.2% vs. 17.6%; hazard ratio [HR]: 0.49; 95% confidence interval [CI]: 0.28 to 0.83; p = 0.009). The intracoronary abciximab bolus did not reduce the primary endpoint in patients without diabetes (7.4% vs. 7.5%; HR: 0.95; 95% CI: 0.68 to 1.33; p = 0.77), resulting in a significant interaction (p = 0.034). Among diabetic patients, intracoronary versus intravenous abciximab bolus was associated with a significantly reduced risk of death (5.8% vs. 11.2%; HR: 0.51; 95% CI: 0.26 to 0.98; p = 0.043) and definite/probable stent thrombosis (1.3% vs. 4.8%; HR: 0.27; 95% CI: 0.08 to 0.98; p = 0.046). At CMR (n = 792), the myocardial salvage index was significantly increased only in diabetic patients randomized to intracoronary compared with intravenous abciximab (54.4; interquartile range: 35.1 to 78.2 vs. 39.0, interquartile range: 24.7 to 61.7; p = 0.011; p for interaction vs. no diabetes = 0.016). Conclusions In diabetic patients with STEMI, the administration of intracoronary abciximab improved the effectiveness of primary PCI compared with the intravenous bolus.