Automated percutaneous lumbar discectomy (APLD) has been developed since 1984 when Gary Onik first attempted it. This procedure has many advantages and has been used widely in the treatment of protruded disc diseases. The success rate of APLD by authors from March 1988 to February 1993 when the discographic computed tomography (CT) had not been performed was 74%. In evaluating lumbar disc diseases, we have used discographic CT. According to the patterns of dye distribution in the disc, two different types of protrusion can be distinguished: broad dye base protrusion and narrow dye base protrusion. From April 1993 to July 1994, 52 patients with protruded disc diseases were performed discographic CT. 23 Patients had narrow dye base protrusion and 29 patients had broad dye base protrusion. 29 patients with a broad dye base on discographic CT were treated with APLD and evaluated. The success rate in these patients was 93% by Macnab's criteria. Thus, we suggest that it is mandatory to apply discographic CT to increase the success rate of APLD in patients with protruded disc diseases.