Eighteen cases of congenital pseudarthrosis of the leg in 17 children were treated by nailing and tibio-fibular graft with a mean follow-up of six years (from one to twelve years). Six patients had reached the end of growth. Primary union was obtained in 17 cases in a mean time of 6.5 months (from 3.5 to 18 months), but one case developed a new pseudarthrosis at the level of an associated upper tibial osteotomy. Only one case required a supplementary graft. Walking was usually achieved without any apparatus after five-and-a-half months, the tibia being protected by a nail which was left in place until the end of growth. In two cases, a fracture produced by trauma occurred in the limb long after consolidation. These two fractures healed in the normal time. Inequality of limb length was present in all the cases, but its progress varied. On three occasions it was treated by femoral lengthening. Stiffness of the ankle and subtaloid joints resulted from nailing of the hindfoot in nine cases and improved very little after freeing of the joints. The use of telescopic rods avoids the need for further operations to change the rod during growth. We consider that this is a reliable method but that, in certain cases, the effects on growth and on the foot can be diminished by appropriate modifications of technique.