Failure of fixation of intertrochanteric fractures that have been treated with a fixed-angle sliding hip-screw device is frequently related to the position of the lag screw in the femoral head. The purpose of this study is to introduce the concept of the tip-apex distance and to demonstrate its clinical usefulness as a predictor of cutout of the screw used for fixation of the intertrochanteric fractures of the hip. The tip-apex distance is the sum of the distance from the tip of the lag screw to the apex of femoral head on an anteroposterior radiograph and this distance on a lateral radiograph after controlling for magnification. To determine the value of tip-apex distance in the prediction of cutout of the lag screw, 67 intertrochanteric fractures that have been treated with a fixed-angle sliding hip screw device were studied. The minimum duration of follow-up was three months during which period all of the fractures either healed or had failure of the fixation. The average tip-apex distance was 21mm (range,22.8-65.8mm) for the successfully treated fractures compared with 35mm (range,8.4-65.8mm) for those in which the screw cutout. There was strong statistical relationship between an increasing tip-apex distance and the rate of cutout. An unstable fracture, a poor reduction were also associated with a significantly increased risk of failure due to cutout.