Spondyloysis is a common condition, but CT findings have been paid relatively scanty attention in journal publication. The authors reviewed lumbar spine CT of 42 patients who were diagnosed as spondylolysis and/or spondylolisthesis in Gyeong Sang National University hospital. the results were as follows. 1. In 27 cases of spondylolysis, it most frequently occurred at L5(55.5%) with 88.3% of bilaterality. The defect of the pars interarticularis was most clearly visible on the slice at or just above the neural foramen. The appearance of the defect had a horizontal plane(88.9%), an irregular surface(85.1%), a non-sclerotic margin(88.9%), and a medial proturbance of the medial aspect of the bone just anterior th the defect(77.8%). spondylolisthesis was associated in 20 of 27 cases(74%), which was demonstrated as an elongation of the anteroposterior diameter of the spinal canal and a pseudobulging disk at defect level in all cases. The degree of the anterior displacement was Grade ulcornerin fourteen(55.6%) and Grade II in five(18.7%) 2. degenerative spondylolisthesis was found in 18 cases and most frequently occurred at L4-5level(88.3%). The characteristic findings were a vertically-oriented joint plane(66.7%), a posterior displacement of the anterior facet with reference to the posterior face(50%), bony spurs in the anterior facet(94.1%), a vacuum facet joint(55.6%), and an increased facet joint distance(50%). 3. Spinal stenosis and disk herniation were two most frequent associated abnormalities. they were found at a rate of 44.4% and 14.8% in spondylolysis and at a rate of 72.2% and 33.3% in degenerative spondylolisthesis. In cases of disk herniation, it frequently occurred just above the level of the defect(2/4) in spondylolysis, in contrast to degenerative spondylolisthesis in which it was most frequent at the same level(4/6). In conclusion, CT must be the highly accurate method for dignosing and evaluating spondylolysis and all types of spondylolisthesis.