This is a retrospective study of 18 patients who had ipsilateral femoral and tibial fractures. They were treated by the retrograde femoral and antegrade tibial intramedullary nail from a single incision in the knee. The average time for union of femoral shaft fractures was 27.6 (18--40) weeks. One patient required antegrade nailing with a bone graft due to metal failure after using the short nail. Two tibial fractures required bone grafting due to bone loss, with an initial open fracture. The average time for union of tibial fractures was 24.5 (18--30) weeks. Functional results using the Karlstrom-Olerud criteria were excellent in 14, good in three, and acceptable in one. The only acceptable result was in a supra- and inter-condylar femoral fracture, with protrusion of the nail tip into the knee joint, which created moderate limitation of knee motion. Simultaneous retrograde femoral and antegrade tibial nailing with a single incision in the knee can achieve satisfactory results in the management of these types of fracture.