High resolution computed tomography is the most accurate diagnostic tool to define a lumbar herniated disc disease because it provides a complete in vivo analysis of bony framework of lumbar spine as well as the supporting soft tissue structures and neural elements. The purpose of this study is to estimate the valve of CT in the evaluation of nerve root compression caused by herniated disc disease. We alalyzed 52 roots of 26 patients of single level herniated disc disease with definite evidence of bilateral or unilateral neurologic deficit who had both CT and myelography at Pusan National University Hospital from May 1983 to March 1987. The results were as follows: sensitivity and specificity of CT is 77% and 81% respectively in the diagnosis of nerve root compression caused by lumbar herniated disc disease. sensitivity and specificity of myelography is 77% and 81% respectively in the diagnosis of nerve root compres-sion caused by lumbar herniated disc disease. The results of this study indicate that high resoluation CT was equivalent to myelography in the diagnosis of nerve root compression caused by lumar herniated disc disease.