CT from fortynine patients with 53 surgical disc explorations were reviewed and correlated with surgical findings. The results were as follows : 1. Frequent locations of HNP were in 14.5(65%) and L5-S1(31%). The most common type of HNP was paramedian type (715). 2. Focal protrusion of the posterior margin of disc and obliteration of epidural fat pad were observed in all of cases (100%) and other common findings were indentation of epidural sac in 46 cases (96%) and compression of nerve root sleeve in 33 cases(69%). 3. Cephalad and caudad extension of protruded soft tissue density in the spinal canal was observed in 15 cases (31%) with variable degree. and more than 6 mm extension were provided to be extruded disc in 9 cases. 4. Vacuum phenomenon was demonstrated in 5 cases(10%) and was accompanied with bulging annulus. 5. Forty eight herniated nucleus(HNP) were confirmed surgically in 44 patients. Misinterpretations were made in 4 instances(4 patients) : 1 because of lumbar s oliosis, 1 because of spondylolisthesis, and the other 2 becasuse of calcified posterior longitudinal ligament and bulging annulus. One cases of true negative examination was central and foraminal stenosis in spinal CT. Thus, sensitivity, specificity and overall accuracy of lumbar spine CT in HNP were 92%, 100% and 92%, respectively.