PURPOSE: Because the prognosis of the mid 1/3 clavicle fracture is good, the conservative treatment with a figure of 8 bandage is the gold standard and the nonunions are rare.However, recently surgical treatment is recommended when the shortening and displacement is severe because of the high nonunion rate and the poor clinical result. This study was undertaken to evaluate that the shortening and displacement at fracture site are associated with the development of nonunion. MATERIALS AND METHODS: We analysed the 194 fractures of mid 1/3 clavicle in adults which had been treated conservatively from February 1993 to January 2002 and did the retrospective study. Of these, 78cases were originally in the middle third of the clavicle and had been completely displaced. We reviewed 63 of these cases. The shortening and displacement at the fracture site was measured on the initial roentgenogram. And the analysis of the patients 'chart was done for another predisposing nonunion factors. Nonunion and delayed union are considered to be present when there has been little or no progression of clinical or radiographic healing at a minimum of 4 months after injury. RESULTS: 15 of the 63cases had developed nonunion.. The average 8.6mm(2mm-17mm) shortening and average 9.7mm(2-22mm) in the union patients. The average 14.5mm(3mm-37mm) shortening and average 17.3mm(4-25mm) in the nonunion patients. We found that initial shortening ≥1 8 m m ( Fisher's exact test, p <0.01) and initial displacement ≥16mm(Chi-square test, p <0.01) at the fracture site were siinificantly associated with the development of nonunion. CONCLUSION: The conservative treatment with figure-8-bandage is the gold standard in the clavicle middle one third fracture. However, the nonunion is commonly occurs in the cases of more of severely shortened and displaced fractures. If there are no signs of callus formation and the patient complains of pain after several weeks, osteosynthesis should be considered.