The authors describe a technique of bone reconstruction after radical resection of bone segments from the distal end of the femur or proximal end of the tibia. This involves the insertion of an intramedullary nail of predetermined length which is fixed to the bone by screws applied at the proximal and distal ends of the nail. An aiming device is used which permits the screws to be applied by a closed procedure. The reconstruction is effected by using the diaphysis of the contralateral fibula, which is divided longitudinally into two halves. These are then applied laterally and medially to the endomedullary nail at the site of the resected area. Grafts of cortico-spongy bone taken from the iliac crests are inserted between the two fibular hemidiaphyses. The authors give a detailed description of the operation and report the clinical results obtained in eleven cases and the complications observed.