169 patients, aged 50 years or older, who were considered surgical candidates for lumbar spinal stenosis (LSS) received either surgical decompression or 6 weeks of physical therapy. Physical function scores (SF-36) were assessed after treatment and during the 2-year follow-up period. Both groups achieved similar improvements in physical function and symptom relief using intention-to-treat analyses and compiler average causal effect with inverse probability analyses to account for cross over between groups. A similar proportion of patients achieved a clinically meaningful level of improvement. It should be noted that 57% of the physical therapy group crossed over to surgery during the trial period.