Arterial complications of thoracic outlet syndrome (TOS) were surgically treated in 11 patients (12 limbs) and venous complications in five (6 limbs). Arteriography showed total occlusion or significant stenosis of the subclavian artery in eight patients (bilateral in 1), with complicating peripheral thrombosis in three. Two patients had unilateral subclavian artery aneurysm: One was the patient with bilateral subclavian occlusion, and the other also had brachial artery embolism. Yet another patient had brachial thrombosis. Treatment included reconstructive surgery (3 limbs), thoracic sympathectomy (3) or decompression alone (6). Of the five patients with venous TOS complications, four were found at phlebography to have subclavian thrombosis and one had significant bilateral subclavian obstruction. Treatment was transaxillary first-rib resection (4 cases) or division of soft-tissue bands and hypertrophied anterior scalene muscle (1 case). After follow-up averaging 9 years, eight of the nine survivors in the arterial group were working and seven were asymptomatic. All five in the venous group were working and only two had slight, strain-related symptoms. Impaired arterial flow in TOS can usually be managed with decompression, but direct surgery (bypass or thrombectomy) or thoracic sympathectomy is required in cases with severe ischemia with proximal occlusion and after resection of a subclavian aneurysm or in cases with unilateral Raynaud's phenomenon or thrombosis of small arteries. For venous symptoms decompression alone suffices.