Over the last two decades, it has become evident that the endothelium is more than an inert, single-cell lining covering the internal surface of blood vessels. Normally, the endothelium actively decreases vascular tone, maintains vascular permeability within narrow bounds, inhibits platelet adhesion and aggregation, limits activation of the coagulation system, and stimulates fibrinolysis. Endothelium dysfunction can be considered present when its functions, either in the basal state or after stimulation, are altered in a way that is inappropriate to the preservation of organ function. Endothelial dysfunction has been associated to many cardiovascular risk factors including diabetes, hypertension and hypercholesterolemia. In addition, endothelial dysfunction may play a crucial role in the development and progression of atherosclerosis. This review will give a brief overview of the different methods to assess endothelial function, and then will focus on the current knowledge on soluble cellular adhesion molecules in relation to the metabolic syndrome and type 2 diabetes.