According to the new concept of the physiology in osteogenesis and the development of external fixation, the excellent results of limb lengthening have been reported. From August 1987 to February 1991, 23 bone segment lengthenings of the upper and lower limbs in 18 pateints were performed using the callotasis with external fixation by Orthofix. The results were summarized as follows:1. The average age was 14 years and 6 months old(range from 6 years and 3 month to 30 years) and the most common cause was the physeal arrest due to trauma(8 cases). The other causes included the physeal arrest due to pyogenic arthritis(2 cases), adolescent tibia vara(4 cases), poliomyelitis(4 cases) and multiple exostosis(2 cases). 2. The lengthening segments were 14 femurs, 5 tibias, 2 ulnas and 1 metatarsal. The average length gained by callotasis was 5.7cm in fumur, 6.2cm in tibia. The healing index was 37,9 in femur, 46.3 in tibia. The index was significantly influenced by age. 3. The complications were analyzed by Paley's criteria, There were 36 problems as pin tract infection, joint stiffness and transient paresthesia and the 6 obstacles, But no complication was experienced. We concluded that the limb lengthening by callotasis might be simple and safe method and all patients were adapted easily to this procedure.