STUDY DESIGN:: A retrospective study. OBJECTIVE:: To analyze the clinical outcomes and radiologic changes following microsurgical bilateral decompression via a unilateral approach in patients with lumbar canal stenosis and degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA:: Satisfactory short-term results have been observed following minimally invasive decompressive procedures, but intermediate and long-term outcomes have not been assessed. It is not yet clear whether decompressive laminectomy with concomitant fusion is the optimal surgical treatment for spinal stenosis combined with mild degenerative spondylolisthesis. We therefore evaluated minimum 3-year clinical outcomes and radiologic changes in patients with lumbar canal stenosis and grade 1 degenerative spondylolisthesis who underwent microsurgical bilateral decompression via a unilateral approach, without fusion. METHODS:: We assessed 21 consecutive patients who underwent surgery conducted by a single surgeon of our hospital, between 2005 and 2007. The Oswestry Disability Index (ODI) was determined preoperatively, just before discharge, and at last follow-up. Plain dynamic x-rays were used to determine slip percentages. RESULTS:: Average patient age and clinical and radiologic follow-up periods were 67 years, 49.3 months, and 18 months, respectively. Preoperative, immediate postoperative, and last follow-up average ODIs were 59.52±9.00, 50.19±7.23, and 26.19±12.42, respectively. But one patient experienced aggravated symptoms and later underwent a fusion procedure. Of the 22 levels with spondylolisthesis, 15 had no sagittal motion as the difference in slip percentage on dynamic x-rays but 7 showed sagittal motion. Average slip percentages increased from 13.90±5.41% to 14.60±5.78% for levels without sagittal motion on dynamic x-ray and from 13.12±3.48% to 18.58±4.55% for levels with sagittal motion. CONCLUSIONS:: Despite small case series with retrospective design and the absence of a control group, our study suggest that bilateral decompression via a unilateral approach in patients with lumbar spinal stenosis and grade 1 degenerative spondylolisthesis showed good mid-term clinical outcomes, despite an increase in slip percentage.However, more marked increases in slippage were observed in patients with sagittal motion in spondylolisthesis levels on preoperative dynamic x-ray than in patients without sagittal motion. Therefore bilateral decompression via a unilateral approach can aggravate symptom related to instability in patients with preoperative sagittal motion on dynamic x-ray and needs longer term follow-up than in our study.