CT from fortynine patients with 53 surgical disc explorations were reviewed and correlated with surgicalfindings. The results were as follows: 1. Frequent locations of HNP were in L4–5 (65%) and L5-S1(31%). The mostcommon type of HNP was paramedian type (71%). 2. Focal protrusion of the posterior margin of disc and obliterationof epidural fat pad were observed in all of cases (100%) and other common findings were indentation of epiduralsac in 46 cases(96%) and compression of nerve root sleeve in 33 cases(69%). 3. Cephalad and caudad extension ofproturded soft tissue density in the spinal canal was observed in 15 cases (31%) with variable degree. And morethan 6mm extension were provided to be extruded disc in 9 cases. 4. Vacuum phenomenon was demonstrated in 5cases(10%) and was accompained with bulging annulus. 5. Forty eight herniated nucleus(HNP) were confirmedsurgically in 44 patients. Misinterpretations were made in 4 instances(4 patients); 1 because of lumbar scoliosis,1 because of spondylolisthesis, and the other 2 because of calcified posterior longitudinal ligament and bulgingannulus. One case 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.