Ossification of the posterior longitudinal spinal ligament (OPLL) was characterized by calcified longitudinal band along the posterior margin of vertebrae, but it has not been possible to know how the cord is compressed within the narrowed spinal canal. Our neuroradiological studies based on CT-view of the 15 cases of OPLL suffering from various degree of myelopathy revealed: 1) Computed tomography precisely delineated shape of OPLL, which was quite polymorphic, like mushroom, irregular cubic and round. OPLL ranged more than two vertebrae was not uniform, but exhibited different configuration at each level. 2) OPLL at lower cervical and higher thoracic regions was difficult to diagnose by conventional lateral roentgenograms, but CT-scan demonstrated clearly whole extent of OPLL. 3) obliteration ratio of the affected spinal canal was calculated on CT-scan. Cases showing severe myelopathy, such as quadriparesis and neurogenic bladder, presented spinal canal stenosis of more than 30%. Spondylosis were concomittant roentgenographic findings on 13 cases of OPLL (87%). However, spondylotic changes responsible to the myelopathy were seen on only three cases. In these case, the obliteration ratio by ossificated ligament was lower than 26%. On conclusion, computed tomographic views of OPLL gave us more detailed information about the stenotic spinal canal and found to be essential examination when considering operative intervention.