The authors report the long-term (more than 10-year) results of cervical laminoplasty for ossification of the posterior longitudinal ligament (OPLL) of the cervical spine as well as the factors affecting long-term postoperative course. The authors reviewed data obtained in 92 patients who underwent cervical laminoplasty between 1982 and 1990. Three patients were lost to follow up, 25 patients died within 10 years of surgery, and 64 patients were followed for more than 10 years. Results were assessed using the Japanese Orthopaedic Association (JOA) scoring system for cervical myelopathy. The recovery rate was calculated using the Hirabayashi method. The mean neurological recovery rate during the first 10 years after surgery was 64%, which declined to 60% at the last follow-up examination (mean follow up 12.2 years). Late neurological deterioration occurred in eight patients (14%) from 5 to 15 years after surgery. The most frequent causes of late deterioration were degenerative lumbar disease (three patients), thoracic myelopathy secondary to ossification of the ligamentum flavum (two patients), or postoperative progression of OPLL at the operated level (two patients). Postoperative progression of the ossified lesion was noted in 70% of the patients, but only two patients (3%) were found to have related neurological deterioration. Additional cervical surgery was required in one patient (2%) because of neurological deterioration secondary to progression of the ossified ligament. The authors performed a multivariate stepwise analysis, and found that factors related to better clinical results were younger age at operation and less severe preexisting myelopathy. Younger age at operation, as well as mixed and continuous types of OPLL, was highly predictive of progression of OPLL. Postoperative progression of kyphotic deformity was observed in 8% of the patients, although it did not cause neurological deterioration. When the incidence of surgery-related complications and the strong possibility of postoperative growth of OPLL are taken into consideration, the authors recommend expansive and extensive laminoplasty for OPLL.