With the introduction of image intensifier in orthopaedic surgery, interlocked intramedullary nailing is one of the most prevailing method in the treatment of long bone fracture especially in femur and tibia. Advantages of this method are rigid fixation of fracture fragment resistant to rotational force, low infection rate, possible early post-operative motion and weight bearing and bone graft effect by medullar reaming procedure. But we had encountered variable complications during and after operation of 63 cases in 59 patients who had undergone interlocking nailing for femur or tibia fractures from Mar 1990 to Feb 1992 at Dae Dong General Hospital. The results were as follows : 1. Delayed union and nonunion developed in nine cases and infection was noted in nine cases, seven of them were superficial infections. 2. Operative complication were encountered with four cases of new fracture, three cases of angolation deformity, four cases of shortening. 3. Four cases of nail profusion was developed because of inadequate implant length. Postoperative metallic failure was found in three cases. 4. Sufficient preoperative planning and skillful technique can decrease the complications.