Objectives: Erectile dysfunction(ED) commonly coexists with coronary artery disease(CAD) and/or risk factors for atherosclerosis. Because the silent or documented atherosclerosis or vascular risk factors are very frequent, the possibility of endothelial dysfunction in ED patients is expected to be increased. Our aim was to evaluate the endothelial functions in patients with vasculogenic ED with vascular risk factors and compare them with age-matched non-ED patients or healthy controls. Design: We studied 36 patients with presumed vasculogenic ED, 39 age-matched patients with similar risk factors without ED and 25 age-matched healthy controls without ED, known cardiovascular disease or risk factors. Erectile function was evaluated by the International Index of Erectile Dysfunction(IIEF) scores. Brachial artery flow-mediated dilatation(FMD) and nitroglycerine-mediated dilatation(NMD) were measured. Results: Baseline demographics were similar except the IIEF score and duration of diabetes in patients with ED. Brachial artery FMD and NMD were significantly reduced in patients with ED(3.2±3. vs. 6±4, p< 0.0001 for FMD, 12.2±6 vs. 15.4±6 p=0.032 for NMD). In patients with similar risk factors but without ED, FMD was significantly lower but NMD were not different compared with healthy controls(6±4 vs. 10.2±3, p< 0.0001 for FMD and 15.4±8 vs. 16.4±6, p=0.81). IIEF scores were weakly correlated with FMD(r=0.25, p=0.028) in patients with ED. There were significant correlations between FMD and NMD in patients with ED(r=0.46, p=0.05) and with risk factors(r=0.72, p< 0.0001) but not in healthy controls(r=0.54, p=0.792). Vasculogenic ED patients have more markedly impaired endothelial and smooth muscle functions compared with patients with similar risk factors but no ED. Objectives: Erectile dysfunction (ED) commonly coexists with coronary artery disease (CAD) and / or risk factors for atherosclerosis. Because the silent or documented atherosclerosis or vascular risk factors are very frequent, the possibility of endothelial dysfunction in ED patients is expected to be increased. Our aim was to evaluate the endothelial functions in patients with vasculogenic ED with vascular risk factors and compare them with age-matched non-ED patients or healthy controls. Design: We studied 36 patients with presumed vasculogenic ED, 39 age-matched patients Erectile function was evaluated by the International Index of Erectile Dysfunction (IIEF) scores. Brachial artery flow-mediated dilatation (FMD) and nitroglycerine Results: Baseline demographics were similar except the IIEF score and duration of diabetes in patients with ED. Brachial artery FMD and NMD were significantly reduced in patients with ED (3.2 ± 3. vs. 6 ± 4, p <0.0001 for FMD, 12.2 ± 6 vs. 15.4 ± 6 p = 0.032 for NMD). In patients with similar risk factors but without ED, FMD was significantly lower but NMD were not different compared with healthy controls (6 ± 4 vs. 10.2 ± 3, p <0.0001 for FMD and 15.4 ± 8 vs. 16.4 ± 6, p = 0.81 IIEF scores were weakly correlated with FMD (r = 0.25, p = 0.028) in patients with ED. There were significant correlations between FMD and NMD in patients with ED (r = 0.46, p = = 0.72, p <0.0001) but not in healthy controls (r = 0.54, p = 0.792). Vasculogenic ED patients have more markedly impaired endothelial and smooth muscle functions compared with patients with similar risk factors but no ED.