OBJECTIVES:: METHODS:: In 100 IBD patients (47 ulcerative colitis (UC) and 53 Crohnʼs disease (CD)) and 50 healthy controls, EPC number, CXC motif receptor 4 (CXCR4) expression, the percentage of apoptotic circulating EPCs, and the number of colony-forming units were evaluated. Endothelial dysfunction was assessed by luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone levels, and in a subgroup of patients, brachial artery flow-mediated dilation (FMD) was measured. Kruskal-Wallis ANOVA (analysis of variance), Mann-Whitney U two-tailed, and Spearmanʼs rank correlation tests were used to assess differences. RESULTS:: EPC number was significantly lower in UC patients (39.6 (95% confidence interval (95% CI): 30.7-48.6)) and in CD patients (43.1 (95% CI: 35.9-50.4)) than in healthy controls (97.1 (95% CI: 88.3-105.9)), (P<0.001). LH and FSH levels and CXCR4 expression on EPCs did not significantly differ from controls. Testosterone concentrations and FMD were lower in UC patients. Number of apoptotic EPCs was higher in both UC and CD patients with an impaired ability to generate colony in vitro. CONCLUSIONS:: We hypothesize that in IBD patients, apoptosis contributes to the reduction of circulating EPC number and to their ability to proliferate in vitro. As this condition represents a risk factor for cardiovascular disease, endothelial function should be evaluated in these patients.Am J Gastroenterol 2009; 104:2500-2507; doi:10.1038/ajg.2009.332; published online 30 June 2009