Recently spondylolysis and spondylolisthesis have become major causes of low back pain in the orthopaedic field and numerous methods have been designed for its treatment. The authors used the LSDS with posterolateral fusion for 12 cases of spondylolisthesis and spondylolysis having low back pain and tenderness, which were operated on during the 4 years from Jan. 1983 to Jan. 1986 at Wallace Memorial Baptist Hospital. The advantages of LSDS with posterolateral fusion are as follows. l. In the case of distraction spondylodesis of interspinous process between L4 and Sl; A. the diameter of intervertebral formaina as well as of the whole spinal canal is widened. B. decompression is accomplished. C. the mechanical stress on the posterior columns of vertebral arch is lessened because the plumb line is anteriorly transferred. 2. Technique of LSDS; the knee-elbow position has the advantages of maximal kyphosis together with expansion of the space between the vertebral arches, as well as a reduction in the tendency to bleed because the blood collects in the abdominal vessels. 3. Internal fixation of grafted bone is not necessary. 4. A large surface area for unit mass of graft is in contact with blood supply. 5. Hypertrophy or displacement of graft can not encroach upon the epidural space; as may occur in certain circumstances following posterior fusion. The results of treatment are follows; l. In the case of improvement of symptoms after facet infiltration and knee-elbow position, satisfa- ctory results after LSDS were obtained. 2. The progression of slipping was not occurred after LSDS. 3. In increased lumbar lordosis, we have noted the instability especially with the changes from the mean values in Fergusons angles. 4. In the slip angle, there is some tendency to the lumbosacral instability correlating with the in- crease in the body weight. 5. We have also noted that the functional result was not closely related with degree of displacement.