Although a number of cases of congenital pseudarthrosis of the clavicle have been described in the literature, they provide little direction for the treatment of this condition when it is associated with thoracic outlet syndrome. The authors describe their experience with such a case in a 20-year-old woman. Symptoms of pain in the ulnar distribution of the right forearm and discoloration of the hand with abduction of the extremity had developed over 3 years. The radial pulse was obliterated by abduction of the arm. Exploration of the brachial plexus revealed a constricting band arising from the distal fragment of the clavicle running to the first rib which, together with the mass of the pseudarthrosis, comprised the thoracic outlet. The patient was successfully treated by division of the fibrous band, reduction of the clavicle, internal fixation with a plate and iliac crest bone grafting. At follow-up the patient had a full range of motion in the shoulder and was asymptomatic.