The endothelium plays a key role in vascular homeostasis through the release of a variety of autocrine and paracrine substances. Endothelial dysfunction can be defined as the partial or complete loss of balance between vasoconstrictors and vasodilators, growth promoting and growth inhibiting factors, proatherogenic and anti-atherogenic factors. Dysfunction of endothelial cells is a systemic process and the initiating event in atherosclerosis and many other diseases, and is important in the ischemic manifestations of the disease process as well. There are different invasive and non-invsive methods to assess endothelial dysfunction. Regarding to the management of endothelial dysfunction, it is complex. Beside medications such as statins, ACE inhibitors, L-arginine, COX-2 inhibitors, lifestyle and diatery modifications should be considered, as well.