BACKGROUND Decompression with fusion is usually recommended in patients with lumbar spinal stenosis (LSS) combined with degenerative lumbar scoliosis (DLS). However, elderly patients with LSS and DLS often have other comorbidities, and surgical treatment must be both safe and effective. The aim of this study was to investigate whether decompression surgery alone alleviates low back pain (LBP) in patients with LSS and DLS, and to identify the predictors of postoperative residual LBP. METHODS A total of 75 patients (33 males and 42 females) with a mean age of 71.8 years (range 53-86 years) who underwent decompression surgery for LSS with DLS (Cobb angle ≥ 10°) and had a minimum follow-up period of 1 year, were retrospectively reviewed using the Japanese Orthopaedic Association scoring system for the assessment of lumbar spinal diseases (JOA score). Radiographic measurements included coronal and sagittal Cobb angles, apical vertebral rotation (Nash-Moe method), and anteroposterior and lateral spondylolisthesis. Logistic regression analysis was performed to investigate the predictors of residual LBP after surgery. RESULTS Forty-nine patients had preoperative LBP, of which 29 (59.1 %) experienced postoperative relief of LBP. Logistic regression analysis demonstrated that the degree of apical vertebral rotation on preoperative radiography was significantly associated with postoperative residual LBP (odds ratio, 8.16, 95 % confidence interval, 1.55-83.81, p = 0.011). CONCLUSIONS A higher degree of apical vertebral rotation may therefore be an indicator of mechanical LBP in patients with LSS and DLS. Decompression with fusion should be recommended in these patients.