Arterial aneurysms (AAs) of the periphery are uncommon, are likely underdiagnosed, and primarily confer a risk for limb loss. This is in contrast to abdominal and thoracic AA, which confer a significant risk to life, depending on size and growth rates. Peripheral aneurysms occur often in patients with more proximal arterial tree AA, and thus evaluation of synchronous disease in these patients is important. A peripheral AA is traditionally defined as an increased size of 150% of the proximal normal artery; for most patients, this is a dilation greater than 1.5 cm for the popliteal artery and ~2.5 for the common femoral artery. This chapter will focus on the modern evaluation and treatment of true peripheral AA, and will not discuss pseudoaneurysms.