Most cases of spondylolisthesis are asymptomatic and successfully managed with conservative treatment. Operation was performed in 20% of symptomatic cases having severe back pain, neurological symptoms and or progressive slipping. Although surgical treatments are divided into decompression and fusion, various methods were tried frorn simple Gill's resection to posterior and/or anterior fusion with instrumentation in case of severe slipping. The authors reviewed 49 cases of symptomatic spondylolisthesis, who were surgically treated, and well followed up at Kang-Nam St. Mary's Hospital during past 6 years from January, 1981, to June, 1987. l. Among 49 cases, 23 were isthmic type and 26 were degenerative in nature, and 40 were females. 24 patients(92.3%) of degenerative type were female over 4th decade. Mean age was 47.9 years. 2. The most common site of involvement was L4–5 intervertebral space(25 cases,; 51.0%). 17 cases(73.9%) of isthmic thpe were involved in L5-Sl intervertebral space, and 21 cases (80.8%) of degenerative type were involved L4–L5 intervertebral space. 3. The symptoms were low back pain, intermittent claudication and sciatica in order of incidence. 4. The average slipping measured by Taillard method was 19.5%, and Meyerding's grade I slipping(69.3%) was the highest in the percentile incidence. The average degree of slipping in isthmic type(23.6%) was greater than that of degenerative type(16.4%). 5. Myelogram mainly showed complete or near complete block in degenerative type and ventral indentation in isthmic type. C–T myelogram showed mainly central stenosis in degenerative type, and nerve root compression in isthmic type. 6. In 9 cases,anterior fusions were done ; 5 degenerative and 4 isthmic. In 37 cases, decompression and posteriolateral fusions were done with or without instrumentation ; instrumented in 11 cases. 7. Clinically, the results were judged as excellent in 16 cases(32.7%), good in 26 cases(53.1 %), fair in 6 cases(12.2%), poor in 1 case(2.1%). Thus, 42 cases(85.8%) were considered satisfactory. The satisfactory results were obtained in 77.8% of anterior interbody fusion cases, 88 5% of posterolateral fusion cases, 90.7% of decompression and posterolateral fusion with instrumentation cases. There was no appreciable difference in clinical results between isthmic and degenerative types. 8. There were no changes in slipping in 35 cases(71.5%), Partial reduction were possible in 13 cases(28.5%), and further splipping developed in a patient who had decompression surgery alone. Among 46 cases of vertebral fusion, complete fusion was obtained in 43 cases(93.5%) within one year. 9. Solid anterior spondylodesis was obtained in all the cases of degenerative type, while in 2 cases(50%) of the isthmic type, graft crumbled with redisplacement and delayed fusion. Through the results, it is concluded that posterior instrumentation may not be essential for the successful spondylodesis in cases of posterolateral fusion, since there was no statistical significance in the results between the instrumented and non-instrumented, and isthmic type and degenerative type, and that anterior interbody fusion is best indicated for the treatrment of the degenerative type and not for the isthmic type. Therefore, if anterior interbody fusion is chosen for the successful treatment of isthmic type, a certain type of internal fixator should be combined.