Eighty-five consecutive patients with various spinal disorders who underwent surgery using the Cotrel-Dubousset pedicle screw system at Kantoh Rosai Hospital between August 1986 and November 1989 were studied. The group included 52 men and 33 women, ranging in age from 19 to 76 years, with an average age of 53 years. The postoperative follow-up period was from 15 to 54 months, with an average of 33 months. The diagnoses were lumbar degenerative disorders in 69 cases (spondylolisthesis in 32, lumbar degenerative spinal canal stenosis without spondylolisthesis in 21, and “unstable lumbar spine” in 16), spinal trauma in 9, spinal deformities in 5 (scoliosis in 3 and kyphosis in 2), and tumor in 2 (1 spinal cord tumor and 1 vertebral tumor). The Cotrel-Dubousset pedicle screw system proved not only to be useful in fixing an unstable spine from the lower thoracic vertebra to the sacrum, as is the case with the other pedicle screw systems, but also to have great advantages for use in various spinal disorders, including reduction of slipped vertebra, correction of spinal deformity combined with a hook system, and for anterior spinal instrumentation. Postoperative clinical results were good in most of the cases, but pseudarthrosis considerably affected the results in a few cases. Therefore, great care must be taken, both strategically and technically, to prevent pseudarthrosis.