Twenty-five femoral shaft fractures in twenty-three patients aged 10-16 years with open epiphyses and treated with flexible intramedullary nailing were studied retrospectively. Clinical and roentgenographic follow-up averaged 28 months. Hospitalization, which included patients with multiple injuries, averaged 11.7 days. Patients ambulated without assist devices as early as 2 weeks postoperatively (average of 7.7 weeks). All fractures healed with no leg length inequality--21 with anatomic alignment and full range of motion of the hip and knee. Three patients sustained intraoperative extension of the fracture resulting in healing with angular or rotatory malalignment. One patient with associated knee ligamentous injury had less than full knee flexion at follow-up. All patients had normal gait (except one patient with residual hemiplegia) and were able to participate in full activities including athletics. Early ambulation and functional recovery with low morbidity and cost suggest that this procedure should be considered for the treatment of femoral shaft fractures in this age group.