Ossification of the posterior longitudinal ligament(OPLL) of the cervical spine is uncommon clinical entity. This disease is characterized by an abnormal longitudinal strip of ossified ligamentous tissue along the posterior margin of cervical vertebral bodies. Ossification may lead to narrowing of the spinal canal, thus causing spinal cord compression. This disease entity has been reported on numerous occasions in the Japanese literature since Tsukimoto published the first case in 1960. It is most frequently seen in Japanese, but reports from outside of Japan are being more frequent now. Here we report a case of tetraparesis without trauma in OPLL of the cervical spine. We performed laminoplasty and the result was excellent. The preoperative Japanese Orthopaedic Association (J.O.A.) score was 0 point and postoperative score was 13 point meaning excellent result. The purpose of this paper is to report that OPLL can be progressed relentlessly to nearly complete quadriplegia without trauma, but with adequate decompression nearly normal function cab be retained.