Study Design:Retrospective, controlled studyObjective:To compare one and two-caged posterior lumbar interbody fusion (PLIF) with local bone grafting for spondylolisthe-sis.Summary of Literature Review:Even though there are many reports on PLIF using cages and local bone grafting, Studiescomparing one and two-caged PLIFs are rare.Materials and Methods:Sixty-three patients who underwent pedicle screw fixated PLIF using cages and local bone grafts werefollowed for more than 1 year. Twenty-five patients had one cage (group I), and 38 patients had two cages (group II). Samplingerror, disc height, sagittal Cobb angle, coronal Cobb angle, fusion rate, Oswestry disability index (ODI), operation time, blood loss,and neurologic complications were assessed.Results:There was no sampling error between the two groups, except with regard to diagnosis: degenerative spondylolisthesis,15 cases in group I and 9 cases in group II; spondylolytic spondylolisthesis, 10 cases in group I and 29 cases in group II(p=0.004). Fusion rates were 87.5% and 88.2% for groups I and II, respectively (p=1.000). More disc height loss occurred in groupI (0.6 mm) than in group II (0.0 mm) (p=0.041). Over-3mm-disc height-losses were noted more frequently in group I (20%) thanin group II (2.6%) (p=0.022). ODI improved from 28.1 to 12.3 (72.1% improvement) in group I and from 29.2 to 12.7 (79.3%improvement) in group II. There were no significant differences in operation time, amount of blood loss, or neurologic complica-tions between the two groups.Conclusion:Unilateral one-caged PLIF with local bone grafting and posterior instrumentation was no different from bilateraltwo-caged PLIF with regard to fusion rates or radiologic or clinical results. The statistically significant differences in discheight seemed to be clinically insignificant. Disc height loss of greater than 3 mm was much more common in group I, with one-caged PLIF.