PURPOSE: To analyze the effect of treatment of unstable intertrochanteric fractures with dynamic hip screw and additional trochanter stabilizing plate. MATERIALS AND METHODS: Among twenty three cases of unstable intertrochanteric fractures treated with DHS and additional TSP between January 2002 to December 2004, seventeen cases over sixty years old were reviewed with minimal follow up of one year. We analyzed the type of fracture by AO classification, the age of patient, sex, the cause of trauma in seventeen cases. We evaluated the lag screw slippage, the change of neck-shaft angle and lateral displacement of greater trochanter, the period of union by comparison of last follow up radiographs with immediate postoperative radiographs. The fixation failure is defined that displacement of lag screw tip is more than 3 mm or cut out of the screw from the femoral head. RESULTS: The period of union was average 12.8 weeks. The lag screw slippage was average 8.22 mm. The change of neck-shaft angle was average 2.66 degree. No lateralization of greater trochanter was noted in twelve cases, but five cases showed average 0.8 mm (range: 0.5~1 mm) of lateral displacement of greater trochanter. There was not fixation failure. CONCLUSION: In unstable intertrochanteric fracture, the addition of a TSP to the dynamic hip screw can decrease a change of neck shaft angle, a lag screw slippage, and prevent lateral displacement of greater trochanter.