Between Aug. 1982 and Aug. 1983, computed tomographies of 52 patients with low back pain or low back pain with sciatica were performed at the Department of Orthopaedic Surgery, Korea University Medical College Hospital. All scans for patients were done on the Siemens Somatom II in the supine position. The auther studied level of hemiated disc, the measurement of herniation of the nucleus pulposus and buldging of the annulus fibrous in the midsagittal line. The results obtained are as follows: 1. Of all 52 patients with low back pain, 34 patients(65.4%) are interpreted as revealing herniated nucleus pulposus or buldging of the annulus, and the others demonstrated the different abnormality of lumbar spine. 2. Among 34'patients with buldging or herniated nucleus pulposus, 16 cases are noted at L4-L5, 12 at L5-S1, 6 at L4-L5 and L5-S1, respectively. 3. Mean size of herniated nucleus pulposus or buldging annulus in patients diagnosed as HNP are 1.04±0. 600 mm at L3-L4, 2.83±1.345 mm at L4-L5, 2.32±1.207 mm at L5±S1 and in patients diagnosed as other different diseases are 0.98±0.668 mm at L4-L5 1 .04+ 0.689 mm at L4-L5,1.03±0.489 mm at L5-S1.