From 1972 to 1982, 455 patients had arthrodesis and other operations with screw-plate internal fixation of the lumbosacral spine. Of these 455 patients, 440-413 of whom had had spinal fusion and 27 of whom had undergone pars interarticularis reconstruction--were evaluated for a mean follow-up period of 31.6 months. The principal indications for single-stage posterior fusion, which was performed in 266 cases, were severe degenerative joint disease and painful spondylolysis, while the primary indications for combined anterior and posterior repair, which was undertaken in 145 cases, were spondylolisthesis and malignant tumors. Two cases had single-stage anterior fusion. Initial anterior surgery was performed to achieve reduction of vertebral displacement, while the posterior approach was carried out to allow for fusion of the posterior joints and for osteosynthesis; specially-designed screw plates were attached to the pedicle for this purpose. The rate of solid fusion was 97.4% in the single-stage posterior procedures and 100% in patients who had been treated by a combined approach. Only five neurologic complications were encountered out of the combined approach (two regressive cauda equina syndromes and three regressive L5 nerve root pareses), and these occurred early in the investigation, when the technique was still being refined. Only six cases of single-stage posterior approach sustained a monoradicular lesion that subsided after the offending bone screw was removed. Such complications can be avoided if the surgeon is thoroughly familiar with the techniques described.