The spondylolysis is a defective ossification in the pars interarticularis of the neural arches without displacement of the vertebral body. The authors analysed 810 lumbar spines of adult Korean laborers on the basis examined to determine the anatomic characteristics of spondylolysis. The following results were obtained. 1. The overall incidence in laborer was 6.8%. 2. The most frequent site of the involvement was the fifth lumbar vertebra. of radiologic study and 3. Spina bifida in spodylolysis was approximately 1.7 times as frequent as is normally expected. 4. Lumbarization in spondylolysis was approximately 5.8 times as frequent as is normally expected. 5. Sacralization was not found in 55 cases of spondylolysis.