PURPOSE: The purpose of this study is to analyze the clinical and radiographic results of treatment of unstable pertrochanteric hip fractures in which the fracture line is extended distally or the width of the canal is wide using a long intramedullary nail. MATERIALS AND METHODS: From January 2005 to January 2010, we conducted an analysis of 20 cases of unstable pertrochanteric hip fractures (over AO/OTA 31 A2.2) treated using a long intramedullary nailing and followed up for more than 12 months. Using postoperative and last follow-up radiographs, we measured TAD, Cleveland index, neck-shaft angle, sliding length of the lag screw, and union time. Clinically, we measured the operation time, the amount of transfusion, and Parker and Palmer's mobility score. RESULTS: The mean bony union time was 16.4 weeks(10-21 weeks). The mean sliding length of the lag screw was 4.3 mm(1-10 mm) and the mean varus angulation after surgery was 5.1degrees(3-8degrees). The mean operative time was 118 min(60-140 min), and the mean transfusion amount was 2.0 pint(0-4 pint). According to Parker and Palmer's mobility score, mean preoperative score was 7.5 points and mean postoperative score at last follow-up was 6.9 points. CONCLUSION: In treatment of unstable pertrochanteric hip fractures, when the fracture line was extended to below the lesser trochanteric level or the medullary canal width was wide, use of a long intramedullary nail showed excellent clinical and radiologic results and can be regarded as a good treatment option.