Sixty-six cases of noninfected nonunions (27 femoral and 39 tibial) were treated with an interlocking nail. In these cases, 92.6% of the femurs and 94.8% of the tibias healed after the first operation in a mean time of 15.4 and 13.0 weeks, respectively. Deep infection complicated five nailings (7.5%, two femur and three tibia), which included three patients with reactivation of latent osteomyelitis. All cases healed after debridement and use of gentamicin PMMA beads. In one case the nail had to be removed and replaced by an external fixator. Residual angulation between 5 degrees and 10 degrees occurred in three femurs and seven tibias. Shortening occurred in all patients and averaged 0.9 cm in the femur and 0.5 cm in the tibia. Of the patients treated for femoral nonunion, 92.5% achieved full hip flexion and 77.8% full knee flexion on final follow-up examination. In patients with tibial nonunions treated with a locked nail, 92.3% had normal knee flexion and 84.6% obtained normal ankle function. Interlocking nailing offers unique advantages to patients with femoral or tibial shaft pseudarthrosis. The technique allows early weight-bearing, range of motion of adjacent joints, and reliable rates of consolidation of the nonunions.