A most common site for the isthmic spondylolisthesis is at fifth lumbar vertebra(L5) and far less at fourth(L4). The pathogenic lesion in the pars interarticularis is essentially the same in LA and L5 isthmic spondylolisthesis, but the clinical characteristics may differ each other according to their anatomical and biomechanical differences. A retrospective review of 24 patients of LA(study group) and 27 patients of L5(control group) isthmic spondylolisthesis was undertaken for their medical records and radiographs to compare the clinical characteristics in each groups. Included in each groups were all patients who were surgically treated during the same period and followed for more than two years after surgery. In the study group, 18 of 24 patients were females having an average age of 42.5 years(ranging 34-65), while in the control group, 17 of 27 patients were males having an average age of 38,1 years (ranging 13-59). The symptoms were severe leg pain in most of the study group, but in the control group, the leg pain and back pain were equally complained. The degrees of slip were similar in two groups, but a narrowing of dise space at slip segment was more prominent in study group. The lateral radiographs taken in flexion and extension revealed more changes of slip in study group (4.7mm in study group vs 2.8mm in control group in averages), and more angular motion at slip segment in study group unless the dise space is not severely narrowed. A spinal stenosis in CT findings was disclosed in almost all patients of study group and in 18 patients of control group. The sizes of L5 transeverse process were bigger than twice as those of L4 in 17(70.8%) patients including 9(37.5%) sacralizations of L5 in suty group, while in control group they were only 8(29.6%) patients with no sacralization. The heights of intercreastal line revealed no difference in two groups. The surgical procedures in study group were fusion only in two and decompression with fusion in 22(91.7%) patients and those in control group were fusion only in 11 and decompression with fusion in 16(59.3%) paticnts. The satisfactory results of treatment were in 21(87.5%) patients of study group and 25(92.6%) patients of control group without significant difference between two groups. In conclusion, the L4 spondylolytic spondylolisthesis compared to L5 lesion was more unstable and developed spinal stenosis more often. The surgical treatment and decompression procedure were also more needed in L4 lesions particularly in agend women.