The authors treatment 35 patients with ossification of the posterior longitudinal ligament(OPLL). Sixteen of these patients had surgery during the past 3 years between 1983 and 1985. In this paper wer present a radiological and clinical analysis of these cases with a literature review. We also discuss a clinical system of grading, different types of radiological patterns, the indications of surgical treatment and the choice of operative methods. 1) The ages of the patients ranged from 31 to 79 with a mean of 55.4 years. 57.1% of the patients were in the sixth decade. The male to female ration was 28:7. 2) The cases were graded on the bases of symptoms. Grade I, no symptoms or mild neck pain, 1 case(2.9%) ; Grade II only radiculopathy, 14 cases(40.0%) ; Grade III, mild myelopathy but able to walk, 11 cases(31.4%) ; Grade IV, severe myelopathy and unable to walk alone, 7 cases(20.0%) ; Grade V, complete paralysis of one or more extremities, 2 cases(5.7%). 3) Lateral tomogram and CT scan were most useful for assesment of OPLL. 4) The pattern of OPLL was divided into a continuous type(25.7%), a multiple segmented type(31.4%), a single segmented type(20.0%), and a mixed type(22.9%). 5) In cases of a clinical grading of more than III, surgery must be considered In grade II, surgery is indicative if conservative management failed to improve the clinical symptoms. 6) Extensive total laminectomies and foraminotomies were found to be advisable in cases of OPLL involving more than two vertebrae. 7) The modified Smith-Robinson approach showed the best surgical results in cases of single segmented OPLL.