Ossification of the posterior longitudinal ligament of the spine is a newly recognized disease entity. Ossification may lead to narrowing of the spinal canal, thus causing spinal cord compression. It is seen most frequently in Japanese, but reportes from outside of Japan are few. Twenty cases with OPLL treated at St. Vincent Hospital between July 1987 and June 1990 were subjected to this study. Operative treatment was performed in 9 cases, 2 anterior interbody fusion, 3 extirpation and anterior interbody fusion, 3 floating and anterior interbody fusion and one laminoplasty. The purposes of this study are (1) to report the radiologic type, the average involved segments of the cervical spine and associated diseases of the ossification of the posterior longitudinal ligament in Korean (2) to describe the result of 9 surgically treated cases. The radiographic analysis of 20 cases showed high incidence in C5 level, segmental type in women. The average involved segments of the spine were 2.3 vertebrae. The most common associated disease was diabetes mellitus. The result of 9 surgically treated cases was satisfactory, so anterior decompression and interbody fusion of laminoplasty could be encouraged to relieve the symptom. The preoperative average Japanese Orthopedic Association (J.O.A.) score was 10.5 points and the postoperative score was 15.5 points.