Endothelial progenitor cells (EPCs) have a role in the repair of endothelial surfaces after injury. Reduced numbers of EPCs are related to endothelial dysfunction and adverse clinical events, suggesting that endothelial injury in the absence of sufficient repair by circulating EPCs promotes the progression of vascular disease or valvular disorder. The aim of the present study was to assess the number and role of EPCs in patients with aortic valve regurgitation (AR).We assessed the number of EPCs and apoptotic EPCs in 31 patients with significant AR and compared them with 30 patients who had similar risk factors and no valvular disease. The numbers of EPCs and apoptotic EPCs were assessed by flow cytometry. The 2 groups had similar clinical characteristics. Patients with AR had fewer circulating EPCs and late apoptotic EPCs as compared with the control group (0.054 ± 0.03% vs. 0.079 ± 0.06%, P=0.039 and 0% (0-3.4%) vs. 5% (0-14%), P=0.03, respectively). In patients with AR, circulating EPCs correlated negatively with septal thickness (r=-0.47, P=0.01), whereas late apoptotic EPCs had a negative correlation with left ventricular end-systolic diameter (r=-0.57, P=0.01).Patients with AR have fewer EPCs and late apoptotic EPCs. These data suggest an impaired valvular endothelial cell regenerative process in patients with AR.