To evaluate the diagnostic value of CT myelography in lumbar disk herniation, we retrospecitively analysed the findings of myelography and CT myelography. Comparisons of the two diagnostic modalities were made in 51 cases of which 47 were confirmed as herniation at surgery. Diagnostic sensitivity of myelography and CT myelography were 76.9% and 90.2%, respectively. Lumbar disk herniations were misdiagnosed in 10 cases of myelography and in 4 cases of CT myelography. CT myelography better demonstrated associated findings such as ligamentum flavum thickening, calcified disk, etc., wihic were often not seen in myelography in 35 cases(68.6%). In conclusion, CT myelography proved to be of higher diagnostic values in the diagnosis of lumbar disk herniation, and demonstrated location of the herniation more accurately than myelography alone. Our findings support the use of CT after plain myelography for the exaet diagnisis of lumber disk diseases.