lent disorder that has a wide range of clinical presentations and variable consequences for the patient. Although atherosclerosis is by far the most common cause of lower extremity ischemia, a variety of other conditions can cause either acute or chronic lower extremity ischemia. Three major factors are contributing to an increase in both the prevalence and incidence of lower extremity ischemia. The first is the general aging of the population in developed countries, with its attendant increase in the prevalence of atherosclerosis, peripheral aneurysms, and other vascular lesions associated with advanced age. The second factor is the alarming increase in the incidence of diabetes, particularly among adolescents and younger adults.As diabetes accelerates the progression of atherosclerosis and lower extremity ischemia, we can anticipate further increases in the number of patients presenting at a younger age with lower extremity ischemia. The third factor is the increasing numbers of patients who have undergone prior peripheral arterial bypass surgery and are potentially at risk for either graft occlusion or progression of disease. At many major medical centers the majority of patients presenting with acute limb ischemia are those with thrombosis of a prior lower extremity arterial reconstruction. This chapter reviews the causes, clinical presentations, diagnostic approach, treatment options, and outcomes of chronic and acute lower extremity ischemia. Etiology and Presentation