PURPOSE: This study was designed to evaluate the clinical effectiveness including bone union, leg length discrepancy, after retrograde flexible intramedullary nailing for pediatric femoral fractures. MATERIAL AND METHOD: Nineteen cases (18 patients) with femur fracture at the age of 4 to 10 years (mean age 6.7) have been followed up over the minimum of one year. Under imaging intensifier, the fracture was temporarily reduced with manual traction, and 1 or 2 flexible nails were inserted at medial and lateral side of distal femur above the distal epiphysis. After two weeks of immobilization with long leg splint, joint motion was permitted. At 6-8 weeks, partial weight bearing was permitted, and at 10- 12 weeks, full weight bearing was permitted. RESULTS: Time to radiologic union averaged 10.9 weeks. Limb length discrepancy ranged from 7mm of shortening to 6mm of overgrowth(mean ; 1.1mm of overgrowth), but there was no severe limb length discrepancy over 10mm. As another complications, there were one case of limited motion of knee joint and one case of broken nail. CONCLUSION: We found that retrograde flexible intramedullary nailing is a safe, effective treatment for acute femoral shaft fractures in skeletally immature patients.