The transpedicular screw fixation is known to be capable of providing more secure correctional, force and rigid fixation to the spine. But it is often accompanied by various complications, including stress shield effects, loosening in osteoporotic spine, pseudoarthrosis, hardware problems and long-term change in motion behaviors at the adjacent motion segment and etc. The purpose of this study is to compare the flexible and rigid rods system in terms of complications and problems for various degenerative lumbar diseases. From September 1991 to November 1994, 41 patients were operated with the flexible rods system (group A) and 39 patients with the rigid rods system (group B). They were followed up for more than 4 years. The flexible rods system was composed of 41 cases of Wiltse system and the rigid rods system was composed of 29 cases of Diapason, 8 cases of TSRH and 2 cases of CD instrument. The resuits of the study were as follows: 1. By standard Cobb lateral measurement, 7 cases in group A and 10 cases in group B showed significant loss of sagittal angle (>4), post-operatively. 2. Hardware failure was noted in 7 cases in group A and 10 cases in group B. In group A, rod bending was seen in 4 cases, rod breakage in 2 and screw loosening in one. In group B, screw loosening was observed in 5 and screw-rod locking mechanism failure in 5 cases. 3. In spondylolisthesis patients, 10 cases in group A and 14 in group B, there was no statistically significant differences between the two groups in the reduction rate immediately after surgery and loss of reduction at the last follow up. 4. Clinical results were good to excellent in 85.4% of patients in group A and 82.1% of group B. No statistically significant differences between the two groups were found, 5. No statistically significant differences between the two groups were found with respect to degenerative changes at the adjacent motion segment to the fused level and pseudoarthrosis.