We analysed 20 cases of clavicular nonunions, treated by internal fixation with plate and bone graft at the Pohang St. Marrys Hospital between 1993 and 1997. Among them, sixteen patients had been treated with conservative method and four with surgery initially. Radiologically, seventeen nonunions were atrophic and three hypertrophic. Interposition of the injured soft tissue, inadequate reduction and insecure fixation were etiologic factors of nonunion in this study. The complete unionswere achieved in eighteen by plating with iliac bone graft and in two by intramedullary fixation with S-pin or Rush-pin each The average time for union was 14.2 weeks. The average length of follow-up was 16.5 months. The complications were limitation of motion in three patients and brachial plexus injury in one. Associated symptoms of the nonunion including pain disappeared in all patients. In this study, we discuss the cause and treatment of clavicular nonunion with specific attention to the rigid internal fixation and the outcome of treatment. We concluded that symptomatic nonunion of the clavicle could be treated by operation, and rigid internal fixation with plate and bone grafts are thought to be a reliable treatment for the nonunion of the clavicle.