Background: There is high incidence of malunion and nonunion after surgical treatment of comminuted sub-trochanteric femoral fractures. Biological fixation can decrease these complications while maintaining the soft tissue vascularity. The purpose of this study was evaluation of the outcomes of bridge plating for treatment of comminuted sub-trochanteric fractures of the femur retrospectively. Methods: Twenty patients with comminuted sub-trochanteric fractures of the femur between 2001 and 2007 were included in this retrospective study. Twelve patients were males and eight patients were females, mean age was 45.6±14.9 years (range: 33-74 years). Thirteen patients with C-3-.1 and seven patients with C-3-.2 type fractures according to AO classification. Under fluoroscopy and according to biological fixation rules bridge plating was performed for all patients. At the final follow-up Pain, hip and knee motions, walking capacity, daily activities, functionality, and radiological assessment were reported for the statistical analysis. Results: The mean period of follow-up was 38.4±13.7 months (range: 24-50 months). The average periods for partial and then full weight bearing were 3.5±1.1 months (range: 1.7- 4.8 months) and 4.5±1.3 months (range: 3-6 months) respectively. The outcomes were seventeen excellent (85%), one good (5%) and two poor (10%) according to Sanders' criteria. With respect to the femoral shaft-neck angles, there was no significant difference between the fractured and healthy sides. Conclusion: Using of bridge plating for biological fixation offered a good alternative technique in the management of comminuted sub-trochanteric femoral fractures. Key Words: Sub-trochanteric femur, biological fixation; comminuted fracture; femur. INTRODUCTION Comminuted sub-trochanteric femoral fractures in adults are high energy injuries. There is discontinuity of the medial cortex due to the injury with important biomechanical consequences. In the proximal femur the medial cortex is subjected to compressive forces while the lateral cortex is subjected to tensile loads during the weight bearing. Comminution and disturbance of medial cortex may result in difficulty of anatomic reduction of this segment. The blood supply for the comminuted fragments is usually compromised in sub-trochanteric area with predominant cortical bone with a less healing power than in metaphyseal area. So, these biomechanical and biological aspects should be considered during preoperative planning of treatment for better outcome.(1-3) The minimal invasive surgery is performed through limited