目的 ： To investigate the state of endothelial function in young ED patients with normal NPTR and to determine the role of NPTR parameters in differentiating underlying vasculogenic ED from psychogenic ED.方法： We retrospectively evaluated 191 ED patients with effective nocturnal penile tumescence and rigidity (NPTR) recording,including detailed medical and psychosexual history,International Index of Erectile Function-5 and vascular parameter.All patients were allocated into psychogenic and organic groups according to the NPTR test.Brachial artery flow-mediated dilation (FMD) was used to diagnose EnD,and ED patients were classified into two groups： non-EnD (FMD≥ 10) and EnD (FMD□10).General and vascular parameters were compared between psychogenic and organic groups,and non-EnD and EnD groups with ED were compared in terms of NPTR parameters.In all,48.7％ and 51.3％ patients were diagnosed as psychogenic and organic ED,respectively.73.1％ of the psychogenic patients had EnD and 39.8％ organic patients had normal endothelial function.结果： In all parameters,only the FMD value showed significant difference between psychogenic and organic ED groups (8.26 ± 2.57 vs 9.16 ± 2.76,P=0.020).No statistical difference was founded in NPTR parameters between non-EnD and EnD groups (P＞0.05).结论： In conclusion,NPTR cannot effectively identify the underlying vasculogenic ED from psychogenic ED.Psychogenic causes may cause or aggravate EnD in these ED patients with normal NPTR.