In lumbar region the epidural fat pad is relatively abundant so that CT can provide sufficient informations indiagnosis of lumbar HNP. Many authors have reported on the CT findings of HNP such as focal nodular protrusion ofthe posterior disc margin, obliteration of epidural fat pad, impingement of dural sac and nerve root, swelling ofnerve root, soft tissue density in the spinal canal and calcificaiton of disc. However three was no proviousreport describing incidence and reliability of these findings. It is the purpose of the present study to surveythe frequency, reliablity, and limitation of these CT findings. The clinical material was consisted of 30operatively porven cases of HNP of the lumbar spine, Each lumbar CT scan was reviewed retrospectively and tefidigns were analysed by two radiologists independently. There were 20 males and 10 females and the mean age was36.7 years. Involvement of L4-5 level was 2.3 times more frequent than that of L5-S1 level. Of 30 cases, 22 wereunilateral posterolateral types and 8 cases central or unilateral far lateral types. CT findings observed werenodular protrusion of the posterior margin of the disc, obliteration of epidural fat pad, impingement of dural sacor nerve root, soft tisssue density in the spinal canal and calcification in the posterior portion of theprotruded disc, in order of decreasing frequency. The conclusions are as follows; 1. Nodular protrusion of theposterior disc margine accompanid by obliteration of epidural fat pad was observed in every case. The formerfinding was designated as direct sign and the latter indirect. 2. Obliteration of the epidural fat appears to besignificant in lateral recesses especially when it occures unilaterally. This was not true, however, in thecentraly located fat pad. 3. Impingement of the dural sac and nerve root were observed in 90% and 67%,respectively, and were very helpful in establishing HNP diagnosis when the direct and indirect signs wereequivocal. Metrizamide CT scan facilitated the evaluation of the dural sac and nerve root. 4. Soft tissue densityin the spinal canal and calcification in the posterior portion of the protruded disc were demonstrated in only 2% and 1% of the cases, respectively.