This study was carried out to assess whether endothelial dysfunction, evaluated by flow-mediated dilation (FMD), is related to the occurrence of the Metabolic Syndrome (MetS) in old age. Eighty patients (25 men and 55 women), mean age 74.1±7.4 years (range 65-99 yrs) were studied. Information on all subjects, medical history and regular medications was obtained. Subjects underwent a clinical examination and laboratory tests. The presence of MetS was evaluated according to the revised NCEP-ATP III criteria. An ultrasound vascular examination (US) of the carotid and brachial arteries was performed in all patients. Intima-media thickness (IMT), presence of plaques (PL), endothelium-dependent (EDV) and -independent vasodilation (EIDV) were also evaluated. Patients were divided into two groups according to the presence/absence of MetS. Significant differences were found between MetS and non MetS patients in: EDV (p<0.01), EIDV (p<0.05) and Homeostatic model assessment index (HOMA) (p<0.02), but not in IMT or PL. MetS was significantly associated with FMD reduction (R 0.4, p<0.005) independently of all possible confounding factors other than EIDV, IMT and PL.