Recent advances in surgical techniques and equipment have made bone lengthening by callotasis both easier and safer, and many successful clinical cases have been reported. The callus formation, however, has often been very poor, and prolonged applied of the external jixator increases the risk of serious complications, such as pin tract infection. We reviewed 68 cases of limb lengthenings performed with callus distraction in 48 patients at Kang Nam St. Mary' s Hospital between January 1989 and May 1994. There were 29 female and 19 male patients, with an average age of 19 (6-50) years. Causes of limb shortening were short stature (14), poliomyelitis (8), fracture and physeal damage (6), osteomyelitis (6), Legg-Calve-Perthe's disease (4), bone tumor (3), congenital dislocation of the hip (3), leg length discrepancy (3), achondroplasia (2) and hip dysplasia (1). Sixty eight calluses were classified radiographically into 6 types: external, straight, attenuated, opposite, pillar, and scattered. The healing indexes and complications following the procedure were evaluated. The mean femoral lengthening was 6.2 (2-10) cm, the tibial 6.5 (3.3-15.7) cm, the forearm 1.8 (1.6-2.2) cm and the humerus 10 cm. Fifteen cases classified as external type, 5 femur, 7 tibiae, 2 forearm and 1 humerus, with healing index of 34 days/cm and no major complications. Thirty one cases classified as straight type, 7 femur, 22 tibiae, 1 forearm and 1 humerus with healing index of 38 days/cm and 2 obstacles. Fourteen cases classified as attenuated type, 4 femur and 10 tibiae with healing index of 47 days/cm and 2 obstacles. Six cases classified as opposite type, 4 femur and 2 tibiae with healing index of 65 days/cm and 3 obstacles and 1 residual complications. Two cases classified as scattered type, 2 tibiae with healing index of 116 days/cm and 5 obstacles. The scattered type of the callus in two cases was suspected to be a result of poor callus formation due to K-wire breakage conditions that autogenous bone marrow transplantations were performed. This classification enabled us to estimate the intrinsic conditions, predict the healing index, incidence of complications, and decide to apply early bone marrow injection to the callus.