Thoracic outlet syndrome (TOS) results from compression of the neurovascular structures that pass through the thoracic outlet. TOS may be classified as neurogenic TOS (NTOS), venous TOS (VTOS), or arterial TOS (ATOS). NTOS presents with upper-extremity symptoms attributable to compression of the brachial plexus. VTOS, also known as Paget-Schröetter Syndrome, involves subclavian-axillary venous occlusion, thrombus formation, and rare embolization. ATOS results from obstruction of the subclavian artery with claudication, thrombus formation, and possible embolization. Adjunct diagnostic studies frequently confirm the diagnoses of VTOS and ATOS, but not of NTOS. Successful TOS treatment depends on the establishment of an accurate diagnosis and identification of causative factors. NTOS should be treated initially with physical therapy, but may require surgical decompression, including first rib excision and scalenectomy. VTOS usually requires urgent thrombolysis, anticoagulation, and surgical decompression. The treatment of ATOS is directed at restoring arterial blood flow in addition to surgical decompression.