STUDY DESIGN: This is a retrospective study. OBJECTIVES: We wanted to compare and evaluate the results of using one cage and two cages with local bone grafting for each segment when performing posterior lumbar interbody fusion (PLIF). Summary of Literature Review: Some authors have reported that unilateral one-caged PLIF with local bone grafting and posterior instrumentation was no difference from bilateral two-caged PLIF regard to the fusion rates and the radiologic or clinical results. MATERIALS AND METHODS: From March 2005 to February 2006, PLIF was performed on 36 patients who had lumbar degenerative disease. They were categorized as the cases for which one cage was used for a segment and the cases for which 2 cages were used for a segment. The clinical and radiological results in each group were compared. RESULTS: There was complete union in 11 segments with using one cage (55%), complete union in 12 segments using two cages (77%) and incomplete unions in 9 segments with using one cage (45%) and incomplete union in 4 segments with using 2 cages (25%), and there wasn't any case of nonunion (p>0.05). The postoperative changes of the intervertebral disc space were a 2.0 mm increase with using one cage and a 2.2 mm increase with using two cages, yet these values decreased by 0.4 mm and 0.3 mm, respectively, on the last follow-up. The mean operation time was 89 minutes for one segment with one cage and 105 minutes for one segment with two cages. The blood loss was a mean of 602 ml with one cage and 802 ml with two cages (p<0.05). There was no significant difference between the one cage group and the two cages group for the Kirkadly-Willis criteria. CONCLUSION: Posterior decompression and PLIF with one PEEK cage for treating degenerative lumbar disease was more effective for the operation time and the amount of blood loss than that with two cages, but the fusion rate, the alteration of the intervertebral disc space, the improvement of pain and the clinical results were no different. However, these results are from short term follow up, so continuous follow up will be necessary in the future for assessing the long term prognosis.