PURPOSE: We analyze the clinical causes and precautions of nail breakage followed by femoral intramedullary nailing MATERIALS AND METHODS: We reviewed 12 cases of nail breakage followed by the femoral intramedullary nailing from Jan. 1993 to Feb. 2001 and for each cases, we analyzed used nail diameter, patient weight and used nail, time to nail breakage and configuration of non-union. We classified fracture site at the time of trauma as proximal 1/3, middle 1/3, distal 1/3, and evaluated gap of fracture site, displacement of fragment after surgery, location and treatment of broken nail on each part, and analyzed the causes of nail breakage RESULTS: The average time of nail breakage was 8.1 months and distal 1/3 fracture were major as 6 cases. Those were mainly comminuted fracture of Winquist-Hansen type II. After surgery, gap of fracture site and displacement of fragment were mostly observed in middle 1/3 fracture and, in the part of middle 1/3, the site of nail breakage took place in fracture site. Especially in the distal 1/3 fracture, nail breakage happened usually in distal first locking screw hole. The causes of nail breakage were inadequately small diameter of nail inserted into the isthmic portion of medullary canal in proximal fracture, inaccurate reduction of fracture site in middle fracture, and the use of short length of nail and its mechanical damage caused by inaccurate insertion of distal locking screw in distal fracture. CONCLUSION: To prevent nail breakage while femoral intramedullary nailing, in proximal fracture, adequate diameter of nail has to be inserted into the isthmic portion of medullary canal. In middle fracture, the accurate reduction of fracture site will be necessary, and the case of distal fracture, enough length of nail has to be used and especially it is important not to cause mechanical injury with the accurate insertion of distal locking screw in nail