Treatment outcomes were compared in two groups of children with femoral diaphyseal fractures which were treated with external fixation (20 fractures) or flexible intramedullary nailing (20 fractures). These 40 children were between 5.4 to 14.1 years of age. The duration of the operation averaged 52 minutes for the external fixator compared with 70 minutes for the flexible nail group. The time taken to gain full weight bearing, full range of movements and return to school was shorter in the flexible intramedullary nail group. There was a higher complication rate in the external fixator group than in the flexible nail group. At final review, three patients in the external fixator group had pain, two had leg-length discrepancy of up to 1 cm, and four had malalignment of 5 degrees -10 degrees. In the nailing group, there were no leg-length discrepancies or malalignments. We recommend the use of flexible intramedullary nailing for fractures of the femoral shaft in children which require surgery, and reserve external fixation for open or severely comminuted fractures.