The purpose of this retrospective study was to evaluate the radiographic and clinical efficacy of uninstrumented facet fusion in elderly patients undergoing lumbar laminectomy for spinal stenosis due to a single-level degenerative spondylolisthesis. Several studies have clearly demonstrated the beneficial effects of concomitant spinal fusion with laminectomy in degenerative spondylolisthesis. Controversy, however, persists regarding the virtues of fusion in this patient population. This study included 62 patients with a single-level grade I or II degenerative spondylolisthesis who underwent laminectomy and uninstrumented facet fusion for unremitting symptoms of spinal stenosis. Group 1 (39 patients) had a fixed degenerative spondylolisthesis with no measurable translation on flexion/extension radiographs, while group 2 (23 patients) had a mobile degenerative spondylolisthesis with preoperative translation. Postoperatively, the 62 listhetic levels were analyzed for radiographic signs of instability on flexion/extension radiographs for a minimum of 24 months. Clinical outcome was assessed in each patient at the time of final follow-up. In group 1 (patients with no preoperative translation), 64% of the index listhetic facet fusion levels had < or = 2 mm of motion on postoperative flexion/extension radiographs, while the other 36% had > 2 mm to < or = 15 mm of motion. Ninety-six percent of patients with < or = 2 mm of postoperative motion were "much better" after surgery, whereas only 50% of patients with > 10 mm of postoperative motion had similar results. Similar trends were also observed in group 2 with 52% of levels having < or = 2 mm motion and patient "much better" outcomes being observed with less motion postoperatively. The overall postoperative radiographic stabilization rate and improved patient outcomes were higher in group 1 than in group 2. In patients undergoing laminectomy for a grade I or II fixed or mobile degenerative spondylolisthesis, concomitant facet fusion decreases motion and stabilizes the spine via a bony fusion or a stable pseudarthrosis. In general, patients with less motion on postoperative flexion/extension radiographs had a better clinical outcome than those with more motion.