Spontaneous thrombosis of the axillary and subclavian venous segments in young, healthy adults (effort thrombosis or Paget-Schroetter syndrome) is a rare but potentially disabling affliction. The diagnosis should be suspected in any young patient presenting with unilateral arm swelling. Typically, the dominant arm is affected, and frequent, repetitive arm use is a common component of the patients' history. Although the diagnosis can often be confirmed with a venous duplex evaluation, the central location of the venous abnormality occasionally mandates cross-sectional imaging or contrast venography to confirm the diagnosis. The underlying pathophysiology of this disorder is felt to be repetitive venous trauma owing to arm motion in the narrow anatomic space between the clavicle and first rib. The treatment of Paget-Schroetter syndrome is controversial and varies according to individual, institutional, and regional preferences. In general, the trend is toward more aggressive endovascular treatment. Prompt anticoagulation is generally accepted as the minimal treatment offered. Catheter-directed thrombolysis has also acquired a prominent role in reestablishing venous patency. The importance of relieving the anatomic compression of the subclavian vein by first rib resection remains controversial, with some experts advocating surgical intervention in all affected patients, whereas others perform this procedure selectively in cases of persistent venous stenosis or ongoing symptoms. Angioplasty with or without stenting is generally discouraged in the absence of anatomic decompression but may play an adjunctive role in patients undergoing first rib resection.