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 backpain. The authors analysed with clinical observations in 88 cases of spondylolysis diagnosed radiographically atB.N.U.H. from Jan. 1977 to Aug. 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 theparesis of lower extremities in 1.2%. 3. The frequent sites of the involvement were fifth lumbar vertebra in83.6%, fourth lumbar vertebra in 9.8%, third lumbar vertebra in 5.5%, first lumbar vertebra in 1.1% and secondlumbar vertebra in zero. 4. Bilateral lesions were in 68.2% and unilateral lesion was 20.9% in the right side and10.9% in the left. 5. The combined abnormal findings of the spine were spondylitis in 36.1%, suspicious H.N.P. in27.8%, 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.