Treatment modalities for herniated lumbar intervertebral disc are the conservative method, chemonucleolysis, percutaneous diskectomy and operation. Conservative treatment is effective in 70–80% of the acute stage and the other 20% requires chemonucleolysis, percutaneous diskectomy or operation. Indications for operation are cases not improved after conservative treatment, recurrent cases and cauda equina syndrome. Mixter and Barr(1934) demonstrated that laminectomy and surgical removal of disc material could relieve symptoms, but spinal segmental instability, incomplete removal of the disc and postoperative adhesion of the nerve root caused low back pain after long-term follow up. Thus, the authors evaluated the plain X-ray and computed tomographic findings in 21 cases of failed laminectomy to determine the cause of failure. The results were as follows ; 1. Among 21 cases, 18 cases complained of low back pain with sciatica and 3 cases complained of low back pain. 2. In all cases, disc space narrowing was detected on plain X-ray. Total laminectomy and diskectomy promote insufficiency and instability of the lumbar and lumbosacral spine. Whenever one attempts to do total laminectomy and diskectomy, it is recommended that spine fusion be performed in same operating field. 3. Several findings were detected on CT scan : 8 disc protrusions in the operation site, 6 disc protrusions in the operation site and spinal stenosis, 4 extradural scars, 1 extradural scar and other site disc protrusion and 2 cases of spinal stenosis and spondyloisthesis. 4. Computed tomography in cases of failed laminectomy offers more information than has been available by any other imaging method