A disease of large- and medium-sized arteries in which the intima (the layer of the arterial wall closest to the lumen) accumulates abnormal patches of lipids and cells that eventually expand to form elevated 'plaques' which can obstruct blood flow.  Established plaques can undergo a series of additional events that increase the patient's chances of serious vascular complications.  For example, plaques may ulcerate and promote thrombus formation; they may break open and shed emboli; they may calcify and further stiffen the vessel wall; they may cause rupture of the entire arterial wall leading to hemorrhage.