The spondylolysis is a defective ossification in the pars interarticularis of the neural arches without displacement of the vertebral body and it sometimes confuses with other spinal lesions complaining of low back pain. The authors analysed with clinical observation in 88 cases of sponlylolysis diagnosed rdiographically at B.N.U.H form January 1977 to August 1978. The results obtained as follows : 1. Among 88 cases of the spondylolysis, the highest incidence of the age was second decade in 55.7%, and the sex ratio was 4.2 to 1 in male to female. 2. The prominant symptoms were a low back pain in 71.6%, the radiating pain with the low backache in 27.3% and the paresis of lower extremities in 1.2%. 3. The frequent sites of the involvement were fifth lumbar vertebra in 83.6%, fourth lumbar vertebra in 9.8%, third lumbar vertebra in 5.5%, first lumbar vertebra in 1.1%, and second lumbar vertebra in zero. 4. Bilateral lesions were in 68.2% and unilateral lesion was 20.9% in the rig t side and 10.9% in the left. 5. The combined abnormal findings of the spine were spondylitis in 36.1%, suspicious H.N.P. in 27.8%, spondylolisthesis in 25.0%, spina bifida in 8.3% and lumbarization in 2.8% in that order. 6. The causes of spondylolysis are still uncertain, but we are experienced 9 cases(10.3%) in the definite history of the trauma.