PURPOSE: To evaluate the causative factors of metal failure after internal fixation, and to suggest more rational treatment guideline that can prevent metal failure in the mid-shaft femur fractures. MATERIALS AND METHODS: A retrospective review of 17 cases, who were treated with internal fixation for the femur mid-shaft fracture was analyzed. We evaluated the cause of injury, fracture type and site, associated injury, used instruments, duration to metal failure, and complications. RESULTS: The metal failure occurred on average 14.8 months after internal fixation. As extrinsic factors, early exercise and weight-bearing in 7 cases, slip down during ambulation in 4 cases, improper physical therapy in 3 cases and unknown cause in 3 cases were related to metal failure. Most metal failure were occurred at the initial fracture site in 12 cases. Other metal failure site were empty holes in 1 case and proximal area of fracture site in 1 case, and screw breakage in 3 cases. CONCLUSION: Accurate preoperative evaluation of fracture site, fracture type and proper selection of instrument, and precise surgical technique will be essential for the prevention of metal failure.