Between 1979 and 1986, 140 patients with fractures of the femur and 94 with tibial fractures were treated with our own interlocking cylinder nail system and followed for 1 to 3 years. Overall, 97.9% of fractures of the femur and 93.6% of the tibia were found to have achieved excellent or good results clinically and radiologically. Complications included: delayed union which developed in 2 patients with femoral and tibial fractures and deep infection which developed in 3 of the tibial fractures. Even in highly comminuted fractures, the fracture site can be fixed securely with the interlocking cylinder nail system. Because mechanical strength of the cylinder nail is by far superior to that of the clover nail, the patient may be allowed early full weight bearing on his affected leg.