Kuntscher introduced the interlocking nail as the name of Detensionsnagel at 1968. Klemm, Kaessman, Hempel used it clinically through transverse hole. Authors tried to make the sagittal hole at the dorsum of the Kiintscher nail, which was interlocked- from the slot to the hole by bone screw. The direction of the sagittal hole crossed right angle to the transverse hole. Analysis of 35 cases conducted following conclusion. 1. Transfixing the screw at the sagittal hole of the nail can be done easily when transfixing through the transverse hole is difficult. 2. There was no difference in stability between transverse hole and sagittal hole transfixation. Lateral movement of the nail was disappeared after transfixation of the screw at the sagittal hole. Interlocking system is very similar to Harrington distraction rod system. 3. One case of nail breakage had occured at the transverse hole. Nail breakage easily occurs if the hole is situated near the fracture site. For prevent nail breakage larger nail insertion is desirable. (More than 14mm in femur and more than 12mm in tibia.) 5. Indication of the I-M nailing is widened by screw interlocking: from the subtrochanteric fracture to the supracondylar fracture of the femur. It is also useful in arthrodesis of the knee joint. 6. Addition of the Interlocking in ordinary I-M nailing patient could walk 3 to 10 days after opera- tion and radiologic union achieved 12 to 20 week after opeation.