For correction of leg length discrepancies and for the treatment of segmental bony defects we used a modular AO-fixator knowing that the principle of the distraction osteogenesis is not dependent of a special fixation device. In our small series the AO-fixator proved to be a good alternative to the ring fixator of Ilizarov for the use on the tibia but not on the femur where we noticed a relatively high incidence of complications, especially deformities of the axis. The distraction osteogenesis has proved to be an efficient technique for limb lengthening and segmental bone transport but is high demanding for the patient and the surgeon.