Ossification of the ligamentum flavum(OLF) is a well recognized cause of acquired spinal canal stenosis resulting in myelopathy, radiculopathy, or a combination of both. OLF is extremely rare in caucasian patients, but is one of the most common causes of compression of the posterior thoracic spinal cord in Japan. In most cases, it has been found in the thoracolumbar regions, and rarely in the cervical region. It is frequently but not alwalys found in association with ossification of the posterior longitudinal ligament(OPLL) and may cause cumulative damage, if comhined with OPLL. We experienced a case of ossification of the ligamentum flavum and posterior longitudinal ligament with sacral radiculopathy, which was treated hy posterior decompressive laminectomy and removal of the ossified ligamentum flavum and posterior longitudinal ligament. The day after operation, the radiating pain and paresthesia dramatically improved.