We report a case of degenerative lumbosacral kyphosis for which posterolateral intervertebral fusion was first performed, but failed to relieve, severe back pain which the patient complained of. We performed posterior wedged osteotomy of L4 and fusion from L2 to S1 using the intrasacral fixation technique. We believe the previous operation failed because maneuvering only the disk region was not enough for improving kyphotic lumbosacral alignment. Intrasacral fixation with vertebral osteotomy is an effective method for the correction of degenerative lumbosacral kyphosis in that it can improve the kyphosis of the lumbar spine, as well as reduce the posterior tiliting of the sacrum which we regard as the 6th lumbar vertebrae. It is for this reason that we chose ISF. One year after the operation, the patient is free from the severe back pain which had prevented him from walking.