Arterial thoracic outlet syndrome (TOS) is a rare condition most frequently observed in relatively young, active, and otherwise healthy individuals. It is typically caused by a bony anatomic abnormality, leading to subclavian artery compression, poststenotic dilatation with aneurysmal degeneration and/or ulceration, and mural thrombus formation with distal embolization to the arm and/or hand. The clinical presentation of arterial TOS occurs in four settings: (1) upper extremity claudication due to fixed or positional subclavian artery obstruction, resulting in exercise-induced arm symptoms of fatigue, muscle cramping, heaviness and pain; (2) acute or subacute upper extremity ischemia due to thromboembolism, resulting in pain, numbness and/or tingling, cold sensation, and a pale or mottled appearance in the hand and/or fingers. (This is often associated with sustained digital vasospasm, which may be complicated by fingertip ulceration or digital gangrene); (3) an asymptomatic pulsatile mass in the supraclavicular space, typically found in association with a cervical rib; and (4) the presence of symptoms of neurogenic TOS in a patient with a cervical rib, with an incidental finding of a subclavian artery aneurysm identified on physical examination or imaging studies. In this chapter, we review the clinical presentation of arterial TOS and use of history, physical examination, and imaging studies to establish a sound diagnosis of this potentially limb-threatening condition.