METHODS A retrospective study. OBJECTIVE The aim of the present study was to identify the clinical and radiological features of low back pain (LBP) that was relieved after decompression alone of lumbar spinal stenosis (LSS) associated with grade I lumbar degenerative spondylolisthesis (LDS). BACKGROUND Although decompression and fusion are generally the recommended surgical treatments of LDS, several authors have reported that some patients with LDS could obtain good clinical results including relief from LBP by decompression alone. The pathogenesis of relief from LBP after decompression is, however, not known. METHODS Forty patients with LSS associated with grade I LDS, who underwent a minimally invasive surgical-decompression were enrolled in the present study. All patients complained preoperatively of predominantly leg-related symptoms and LBP (≥ 4 points on Numeric Rating Scale). Clinical and radiological assessments were performed 1 year after surgery (a relief of LBP: Numeric Rating Scale reduction ≥3 points and valuation ≤3 points) and at the last follow-up. We conducted a comparative study between patient groups with and without the relief from LBP (groups R and N, respectively). RESULTS Twenty-nine patients were distributed to group R and the remaining 11 patients to group N. Preoperatively, there was a significant difference between the two groups for age and radiographic flexibility for lumbar extension. Postoperatively, there was a positive correlation between improvement in both LBP and leg symptoms. The clinical outcomes of group R were significantly better than those of group N throughout follow-up period (mean 37 mo). In group R, sagittal lumbopelvic radiographic parameters improved significantly after surgery. CONCLUSIONS Although the causes of LBP are varied in each patients, our results show that concomitant LSS itself might cause LBP in some patients with grade I LDS, because it involves impingement of the neural tissue and discordant sagittal lumbopelvic alignment. METHODS 3.