Although there are several studies regarding the association between RDW and the vascular events, information is scant about possible role of RDW in cardiovascular system. We aimed to investigate whether RDW is related with the severity and extent of angiographically assessed coronary artery disease (CAD). Two hundred ninety and six stable eligible patients who had undergone coronary angiography with a suspicion of CAD were enrolled consecutively. Two hundred and nine (71%) of 296 patients had CAD (men 70%, mean age±SD: 61±11yrs) and 87 patients (29%) had normal coronary arteries (NCA) without any atherosclerotic lesion (men 48%, 52±11yrs). Red blood cell distribution width values were significantly different among the subgroups determined for the severity and extent of CAD. When 14.8% was accepted as the cut-off value for RDW, the sensitivity and the specificity for the detection of CAD was 68% and 52%. When we performed multiple logistic regression analysis to determine the independent predictors of CAD, we found a positive independent relationship between age, gender, family history of CAD and RDW and CAD. Our results show that RDW has a significant relationship with CAD independent of nonspecific inflammation and circulating inflammatory cells. Although we cannot conclude the underlying pathologic process of RDW, we believe that these findings may pave the way for further studies searching the role of RDW in atherosclerosis.