Abstract: Objective:To analysis the main causes of intraoperative periprosthetic femur fractures in congenital dysplasia of the hip（CDH） and summarize the experience of prevention.Methods: A retrospective analysis was taken to 32 cases of CDH patients who have intraoperative periprosthetic femur fractures from Jan 2002 to June 2007.Results:Intraoperative femur fracture occurred in 32 cases（9.3%）of 345 CDH hips.All patients were followed-up.The mean follow-up time was 27.8months（range,5-47 months）.There were 26 Mallory typeⅠfractures and 6 typeⅡ fractures.There was no typeⅢ fracture.All fractures were fixed during operation,and 31 cases healed except 1 case.The postoperation mean Harris score was 91.Conclusion: Cementless prosthesis,subtrochanteric osteotomy,inappropriate choice of prosthesis type and size,proximal femur anatomical abnormal are the main cause of femur fractures in total hip arthroplasty of CDH patients.Consummate preoperative planning,excellent exposure and prophylactic cerclage wires fixation are recommend to reduce this risk.