Ossification of the posterior longitudinal ligament (OPLL) is a degenerative disease of the spine, usually found in the cervical vertebrae. Most symptomatic patients present with a myelopathy or myeloradiculopathy. Surgical decompression is the preferred treatment. The choice of operative approach, anterior or posterior, is still controversial. From January 1986 to June 1992, 20 patients with this condition received operations at Chang Gung Memorial Hospital. The clinical manifestations and the results of treatment are analysed. The ideal surgery seems to be the anterior approach with bone fusion. If, however, the OPLL involves more than three segments, the posterior approach with an expansive laminoplasty would be the better alternative technique.