73 adult patients with isthmic spondylolisthesis were randomized to be treated with either the posterior lumbar interbody fusion technique (PLIF) or the transforaminal lumbar interbody fusion (TLIF) technique. The purpose of this study was to compare the two methods in their clinical and radiographic outcomes over a 2-4 year follow-up. While results demonstrated significantly longer operative times and higher blood loss in the PLIF group compared to the TLIF group, no significant differences were found between groups for any clinical or radiological outcomes over the follow-up period.