OBJECTIVE: The purpose of this study is to compare the outcomes of two methods for stabilization and fusion: Postero-Lateral Fusion (PLF, pedicle screw fixation with bone graft) and Posterior Lumbar Interbody Fusion (PLIF, cage insertion) for spinal stenosis and recurred disc herniation except degenerative spondylolisthesis. METHODS: Seventy one patients who underwent PLF (n=36) or PLIF (n=35) between 1997 and 2001 were evaluated prospectively. These two groups were compared for the change of interbody space, the range of segmental angle, the angle of lumbar motion, and clinical outcomes by Prolo scale. RESULTS: The mean follow-up period was 32.6 months. The PLIF group showed statistically significant increase of the interbody space after surgery. However, the difference in the change of interbody space between two groups was insignificant (P value= 0.05). The range of segmental angle was better in the PLIF group, but the difference in the change of segmental angle was not statistically significant (P value=0.017). Angle of lumbar motion was similar in the two groups. Changes of Prolo economic scale were not statistically significant (P value=0.193). The PLIF group showed statistically significant improvement in Prolo functional scale (P value=0.003). In Prolo economic and functional scale, there were statistically significant relationships between follow-up duration (P value<0.001), change of interbody space (P value<0.001), and range of segmental angle (P value<0.001). CONCLUSION: Results of this study indicate that PLIF is superior to PLF in interbody space augmentation and clinical outcomes by Prolo functional scale. Analysis of clinical outcomes showed significant relationships among various factors (fusion type, follow-up duration, change of interbody space, and range of segmental angle). Therefore, the authors recommend instrumented PLIF to offer better clinical outcomes in patients who needed instrumented lumbar fusion for spinal stenosis and recurred disc herniation.