Acute ischemia of lower limbs is severe: 25% lethality, 34% amputations (mean of 42 recent statistics). Initial clinical examination is the main point: it diagnoses acute ischemia, localizes the point of occlusion, picks up etiologic informations, assesses the repercussion of ischemia on the local and general status. The therapeutic decision is an emergency. Some particular aspects are pointed out: diagnostic between embolization and thrombosis, arterial spasm, distal ischemia with present pulses ("blue toe syndrom"), arterial dissections, complications of aneurysms. Prognosis depends on age, general condition, localization of ischemia, status of the limb, multiplicity or recurrence of embolization, but above all on early diagnostic and therapeutic.