Interlocking intramedullary nailing has many advantages for long bone fracture. However, we can meet many problems during the operative procedure. Among the patients who were treated with interlocking intramedullary nailing from March, 1990 to December, 1991, forty-eight patients(49 cases) of femur and tibia fracture who were followed up more than twelve months(average 14months: 12months 18months) were included in this study. 1) Forty-nine cases consisted of 20 cases(41%) of femur fracture and 29 cases(59%) of tibia fracture. 2) Two cases of proximal protrusion were developed because of inadequate implant length. 3) Operative complications were encountered with 3 cases of new fracture line, 1 case of new fragmentation, 1 case of reduction loss, 2 cases of failure of proximal targeting, 3 cases of failure of distal targeting, 2 cases of distraction of fracture site more than 3 mm, 1 case of sciatic nerve injury due to excessive traction and 1 case of tibial inlet error. 4) Postoperative complications were encountered with 1 case of distal targeting screw failure, 4 cases of infection and 8 cases of delayed union. 5) According to the result, sufficient planning and confirmations(preoperatively, intraoperatively and postoperatively) can diminish the complications. And then the interlocking intramedullary nailing will be useful method in the case of long bone fracture when the operator has extensive experiences.