Red cell distribution width (RDW) is an indirect marker of inflammation and an independent predictor of long-term mortality. The aim of this study was to determine RDW values in patients with ST-elevation acute myocardial infarction (STEMI) submitted to primary percutaneous coronary intervention (PCI) and evaluate its association with adverse outcomes. We measured RDW in STEMI patients before undergoing primary PCI and divided into low and high RDW. Patients were followed up to 3 years after their discharge for the occurrence of in-hospital, 30-days, and long-term major adverse cardiovascular events (MACEs) and mortality. We included 485 patients with a mean age of 61.1(±12.5) years, 62.9% were male. In multivariate analysis, RDW remained independent predictor of long-term mortality and MACE [relative risk (RR) 1.51; 95% confidence interval (95% CI) = 1.11-2.05; P = 0.007 and RR = 1.42; 95% CI = 1.30-1.82; P = 0.004. Area under the curve for long-term mortality was 0.65 (95% CI = 0.61-0.69; P < 0.0001). RDW < 13.4 had a negative predictive value of 87.4% for all-cause mortality. Patients who had worse outcomes remained with higher values of RDW during the follow-up. In conclusion, high RDW is an independent predictor of long-term mortality and MACE in patients with STEMI undergoing primary PCI. A low RDW has an excellent negative predictive value for long-term mortality. Patients with sustained elevated levels of RDW have worse outcomes at long-term follow-up.