Venous thoracic outlet syndrome (V-TOS) and associated subclavian vein thrombosis (SVT) result in significant patient morbidity and can be difficult to manage. Previous studies have suggested that both mechanical compressive factors and pathological alterations in patient coagulation may contribute to the development of SVT; however, no study has specifically evaluated the role of thrombophilia in the treatment of V-TOS and the need for long-term anticoagulation as an adjunct to surgical decompression. This retrospective study describes the clinical courses of 18 patients treated for V-TOS with and without acute SVT. In this review, 67% of patients with SVT are found to have relatively common coagulation disorders and 90% of postoperative complications were associated with some form of thrombophilia. This study suggests that thrombophilia may play an important role in the pathogenesis of V-TOS and may be a determinant of the success of surgical decompression. Clotting disorders should therefore be aggressively evaluated in this patient population and can improve therapeutic outcome.