Closed intramedullary nailing of the femoral shaft fracture is considered to be a standard procedure. Although this procedure has the advantage of high union rate and low complication rate, but complications still exist. We report two cases of iatrogenic femoral neck fracture in a series of 238 femoral shaft fractures treated with interlocking nail. The iatrogenic neck fracture was treated with Knowles' pins after fixation of the femoral shaft fracture with interlocking nail. The prognosis of iatrogenic femoral neck fracture appeared to the time to fixation after the neck fracture. Carefully handling each procedure in femoral shaft nailing is the only way to avoid this complication.