A retrospective study was undertaken to define the factors that cause the neurogenic symptoms in 18 cases of spondylolytic spondylolisthesis who were operated for leg pain and neurologic deficits of motor functions documented by neurologic examination or electromyographic findings in the Department of Orthopaedic Surgery, Fatima Hospital, Daegu for three years since June, 1986. The cases having other combined pathology to cause neurogenic symptoms were excluded. The causes were predetermined by preoperative x-rays, myelograms, electromyograms, and computerized tomograms and the causes were explored at surgery regarding the preoperative findings. The findings were compared with the avilable findings of 13 cases who were operated for low back pain only without any neurogenic pain in the leg during the same period. The cases were quite older and had narrower disc spaces than the back pain group but there were no significant differences in the degree of slipping and stability of slipped level between the two groups. The foraminal stenosis was found in all of the cases and a central stenosis was combined in a case. The intervertebral foramens were narrowed up-down in most of the cases between the bony prominence of proximal pars interarticularis above and the disc and vertebral body below but three cases had soft tissue mass only at the isthmic defect encroaching the foramen. There were hypertrophy of bone and/or soft tissue at the pars interarticularis in all cases. The nerve roots were mainly compressed up-down below pars interarticularis in the foramen in 8 cases and impinged at the anterior foramen in front of the pars interarticularis in 10 cases. The central stenosis was due to marked bony hypertrophy of pars interarticularis and osteophyte of vertebral body. The causes of neurogenic symptoms in spondylolytic spondylolisthesis were foraminal stenosis due to hypertrophy of bone and/or soft tissue at the pars interarticularis combined with narrowing of disc and seemed to be a process of degenerative changes occurring at the motion segment of slipped level.