Red blood cell distribution width (RDW), which is routinely reported in complete blood counts, is a measure of the variability in size of circulating erythrocytes. RDW is a novel, independent predictor of prognosis in patients with cardiovascular diseases. The aim of the present study was to evaluate the significance of this biomarker in a relatively large cohort of patients, and to assess its association with a more severe underlying cardiovascular disease. A cohort of 3,222 consecutive patients undergoing coronary angiography was divided according RDW median. The association between RDW and 3-year outcome in the context of other predictors was assessed using Cox's proportional hazards analysis. Patients with elevated RDWs were older, had higher body mass indices, and had more cardiovascular risk factors and more cardiovascular diseases. The total rate of mortality, MI and stroke (MACE) was 7.7% (120 events) in the lower RDW group, and 18.2% (303 events) in the higher RDW group, p < 0.001. Following adjustment for multiple background risk factors, medications, and laboratory results, the RDW value was independently associated with worse outcome (HR = 1.12, 95% CI 1.07-1.18, p < 0.001, for each 1% increase in RDW). Elevated RDW values are independently associated with adverse 3-year outcome in patients undergoing coronary angiography.