A progressive bone lengthening procedure according to the Wagner and Ilizarov technique and our own protocol was performed on 24 children (32 bones). Wagner's (transverse midshaft osteotomy, intraoperative lengthening of 1 cm and postoperative distraction of 1 mm/day) led to a marked reduction in osteogenic capacities. Patients operated on according to the Ilizarov technique had osteogenic reactions in the medullary cavity and on the posterior aspect of bone segments. Our own method, which included bone decortication, 5–7 days of neutral fixation without distraction, led to massive bone production in the medullary canal and around the bone segments. Rigid osseous bridging was present as early as 3 months after surgery. Neither the type of external fix-ator nor the location or shape of osteotomy had any specific influence on this massive bone reaction. Osteogenesis in limb lengthening is thus closely related to surgical management.