Background It has been reported that increased red blood cell width (RDW) is a marker associated with the presence and adverse outcomes of various cardiovascular diseases.The aim of the present study was prospectively evaluate the severity of coronary artery disease (CAD) and RDW in a large Chinese cohort.Methods A total of 677 consecutive individuals who underwent coronary angiography due to the presence of angina-like chest pain and/or positive treadmill exercise test were enrolled in this study.All patients received coronary angiography and were then divided into two groups based on the results of coronary angiography (CAD group (n=499) and control group (n=178)).The clinical information including classical CAD risk factors and RDW were analyzed to identify their relationship to CAD.The severity of CAD was evaluated by Gensini score and its relationship with RDW was also analyzed.Results Patients with angiographic CAD had significantly elevated RDW levels compared with controls ((12.95±0.77)％vs.(12.73±0.83)％,P=0.001).There was a significant positive correlation between RDW and the Gensini score (r=0.37,P ＜0.001).In multivariate Logistic regression analysis,RDW was demonstrated to be an independent predictor for both angiographic CAD (OR=1.34,95％ CI.1.02-1.77,P ＜0.05) and for a higher Gensini score (＞13,OR=2.23,95％ CI.1.62-3.08,P ＜0.001).In a receiver operating characteristic (ROC) curve analysis,an RDW value of 12.85％ was identified as an effective cut-point in predicting the presence or absence of CAD with a sensitivity of 50.0％ and a specificity of 65.2％.Conclusion RDW is associated with both presence of CAD and the severity of coronary stenosis,suggesting that it might be a readily available marker for the prediction of CAD and its severity.