We aimed to study the vascular reactivity of young male hypogonadal hypogonadism patients without any cardiovascular risk factors and compare these findings with the ones of age-matched healthy controls. Study population consisted of 26 young male hypogonadotrophic hypogonadism patients (20.9 +/- A 1.3 years) and 25 age-matched healthy male controls (21.8 +/- A 2.9 years, P = NS). In addition to detailed hormonal analysis, each subject underwent ultrasound study of right brachial artery. Vessel diameter was measured at rest, during reactive hyperemia [endothelium-dependent flow-mediated vasodilation (FMD)] and after sublingual nitroglycerin administration (endothelium-independent vasodilation). Both flow-mediated and endothelium-independent sublingual nitroglycerin mediated dilatation values of patients were higher compared to controls (12.98 +/- A 10.76% vs. 7.92 +/- A 1.96%, P = 0.003 and 21.44 +/- A 10.36% vs. 14.72 +/- A 3.57%, P = 0.023, respectively). Linear regression analysis revealed that only serum HDL levels (relative risk 2.94, 95% CI 0.12-0.66, P = 0.006) and baseline vessel diameter (relative risk -2.77, 95% CI -17.73 to -2.70, P = 0.009) were found to be independently associated with FMD values. Endogenous male sex hormones seem to exert negative effects on vascular reactivity parameters and much of their effects are indirect that is by the way of alteration on lipid profile.