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Introduction Vascular endothelial production of nitric oxide (NO) plays an important role in the modulation of vessel tone and structure, protecting the vascular wall from atherosclerosis. In pathological conditions, however, the endothelium also produces pro-atherogenic substances (mainly reactive oxygen species), which inactivate NO. The Endothelial dysfunction, induced by reduced NO availability, is known to contribute to the development and progression of vascular damage. For this reason, endothelial function has been a major focus of cardiovascular research in the last few decades. Because NO has a very short half-life and its in vivo measurement is difficult, many researchers prefer to measure its biological activity, particularly the NO-dependent vasodilation, at the level of the coronary and peripheral circulation by endothelial stimuli. The most widely used technique involves measurement of brachial artery flow-mediated dilation. This test allows non-invasive evaluation of endothelium-dependent vasodilation in the peripheral macrocirculation induced by a mechanical stimulus (increase in shear stress caused by 5 minutes of forearm ischemia). The vasodilatatory response is reduced in the presence of major cardiovascular risk factors, particularly essential hypertension. Conclusions Studies conducted mainly in high-risk patients have demonstrated that endothelial dysfunction within the coronary or peripheral circulation is predictive of cardiovascular events (independently of classical risk factors). Drug therapy can improve endothelial function by increasing the availability of NO (a possible adjunctive benefit in terms of preventing vascular damage and improving the prognosis). Future studies will establish whether the evaluation of endothelial function by non-invasive, standardized, reproducible, low-cost techniques is an important test for cardiovascular risk stratification in clinical practice.