Two hundred and sixty seven patients with lumbar spinal stenosis and degenerative spondylolisthesis were randomized to undergo decompression surgery (n=134) or decompression surgery with instrumented fusion (n=133). The primary outcome of interest was the percentage of patients achieving a reduction in score of 30% or greater from baseline to 2-year follow-up on the Oswestry Disability Index (ODI). Secondary outcomes of interest included the mean change in ODI score, the Zurich Claudication Questionnaire, leg and back pain, the duration of surgery and hospital stay and reoperation within 2 years. The percentage of patients meeting the predetermined reduction in ODI scores was similar between groups demonstrating non-inferiority of decompression alone. Surgical time and length of stay was shorter in the decompression group. Reoperation rates were similar between the decompression alone group compared to the fusion group (12.5% vs. 9.1%).