OBJECTIVE: In rare cases, space-occupying pseudoarthrotic clavicular nonunion causes symptomatic brachial plexus compression. The surgical treatment of clavicular pseudoarthrosis has been extensively reported in the literature. This article reports our experience of a definitive treatment strategy using free vascularized fibula flaps in cases of persistent compression of the brachial plexus by relapsing bony nonunion mass lesions. METHODS: Six men (age range, 46-59 yr) and two women (ages 48 and 52 yr) with nonunions of clavicular midshaft fractures were referred between August 2001 and March 2005 because of progressive compression of the subclavicular neurovascular bundle. All of them had displaced traumatic clavicle fractures that had been treated previously at other institutions. At least two surgical reconstructive procedures had been performed beforehand. Four patients had motor deficits owing to compressive brachial plexus lesions; all showed symptoms of combined thoracic outlet syndrome. Our surgery consisted of resection of the space-occupying clavicular pseudoarthrosis (all eight patients), external neurolysis of the brachial plexus (four patients) and reconstruction of the resulting bone defect with free vascularized fibula flap secured with plates (all eight patients). Vascularity of the bone flap was studied using three-phase bone scintigraphy. RESULTS: All patients became free of pain symptoms after surgery. Muscle strength in two of the four patients with preoperative motor deficits improved to normal within 3 months; the other two patients required 6 and 8 months, respectively. Three-phase bone scintigraphy showed adequate perfusion of the bone flaps in all patients. Postoperative bleeding at the recipient site occurred in three patients; these required revision. One patient showed an osseosubcutaneous fistula 6 months after surgery, which was treated conservatively. There was no recurrence of pseudoarthrosis or neurovascular compression at a mean follow-up period of 38.5 months. CONCLUSION: Recurrent space-occupying pseudoarthrosis of the clavicle complicated with neurovascular compression might warrant definitive reconstruction using a free vascularized bone flap.