Fractures of the clavicle, particularly those which are markedly displaced, may, in rare instances cause injury to the subclavian vessels and the brachial plexus which manifest progressively days or weeks after the initial trauma. More often than not, however, a costo-clavicular compression syndrome appears months or years after the clavicular fracture as a result of constriction by scar which invests the neuro-vascular bundle, by a secondary aneurysm or by hypertrophic callus. The authors report 16 such cases, one of which was treated conservatively, thirteen treated by surgical intervention while two cases are awaiting operation. These patients represent just over 1% of brachial plexus lesions seen over a period of twenty years in two surgical centres. Operative treatment consists of reduction of the clavicular deformity, possibly first rib resection, liberation of the plexus and correction of a vascular lesion as required. The outcome is usually good.