Endothelium plays a primary role in the control of vascular function and structure by protective properties of nitric oxide, which have stimulated the development of methods to assess of endothelial function. Flow-mediated dilation is the most widely used method to test endothelial function since it is non-invasive, and measures by ultrasounds the response to increased shear stress, commonly in the brachial artery. This review focuses on available evidence on FMD, which has been tested for the association with risk factors, target organ damage and the predictive value for future cardiovascular events. FMD has been studied widely in clinical research as it enables serial evaluation, also testing the effect of lifestyle and pharmacological interventions on endothelial function at an early preclinical stage, when the disease process is most likely to be reversible. Despite these advantages, endothelial tests, including FMD, are not yet recommended by guidelines for cardiovascular prevention, for the absence of clear additional prognostic value and particularly the poorly standardized non-invasive methodology. However, recent multicenter studies suggest that accurate methodology ensures reproducible FMD measurements, which can be used in future clinical research to test whether interventions ameliorating FMD function are associated to better cardiovascular prognosis.