Conservative treatment is ineffective for ossification of the posterior longitudinal ligament (OPLL) in the thoracic spine, and surgical treatment is indicated for most cases, while such cases are not often experienced. In the present study, the results of surgical management involving mainly posterior decompression for this disease were evaluated clinically. The study included 9 patients (1 man and 8 women) who underwent surgical treatment for OPLL of the thoracic spine between 1984 and 1993. Laminectomy was performed in 5 patients, and laminectomy plus anterior decompression of the OPLL via the posterior approach based on Otsuka's method was performed in 2 patients. In 1 patient, laminoplasty for OPLL of the cervical spine was combined with laminectomy of the symptomatic lesion in the thoracic spine. One patient underwent anterior decompression and fusion. The results were evaluated using the Japanese Orthopaedic Association score (JOA score) and recovery rate. The postoperative follow-up period ranged from 1 year to 10 years and 3 months (mean, 4 years and 6 months). The mean JOA score was 4.8 before surgery and improved to 7.6 at the final examination. This was a mean recovery rate of 50.1%. Symptoms caused by OPLL in the thoracic spine can be alleviated by posterior decompression where OPLL extends from the upper to the middle thoracic spine or extends from the middle to the lower thoracic spine. It seems, however, that OPLL localized to the middle thoracic spine requires anterior decompression.