PURPOSE: To assess the meaning of the unstable intertrochanteric fracture of femur with involvement of lateral cortex by analysing the radiologic result of the surgical treatment using a compression hip screw. MATERIALS AND METHODS: Classifing patients (who has taken the surgical treatment for intertrochanteric fracture of femur using compression hip screw from January 1999 to June 2002) in our hospital with 24 patients who had not much difference statistically in the compression screw located within the femur, Tip-Apex distance (TAD) the Singh Numerical Value of osteoporosis. The results were divided into two groups, group A (without fracture extends through lateral cortex of femur: 16 cases) and B (fracture extends through lateral cortex of femur: 8 cases), when analyzing it. And then analyzed the final examination in the evaluation of electrical potential level by radiology, change of the inside and outside of neck-shaft angle, descent level of the screw and the change of the neck-shaft angle. RESULTS: In the latest follow up, the sliding amount of the screw in group B, the average was 14.9±9.3 mm, and 6.7±3.6 mm in group A. There was no difference statistically (p value>0.05). In the varus change in group B, the average was 8.00±8.12degrees and in group A it ws 2.75±2.63degrees There was statistical difference(p value<0.05). In displacement after operation, it was 7.60±2.61 mm in group B and 0.5±1.80 mm in group A. There was statistical difference (p value<0.05). CONCLUSION: The intertrochanteric fracture with involvement of lateral cortex of femur have to be considered as unstable fracture having tendency of displacement.