Background: The value of lumbar spine arthrodesis in older patients is not well documented. As most of the literature regarding lumbar arthrodesis in older patients has focused on the prevalence of complications, the purpose of this study was to determine the clinical outcomes for older compared with younger patients undergoing lumbar arthrodesis. Methods: We studied 224 patients who underwent a single-level posterolateral lumbar arthrodesis with an iliac crest bone graft. Outcome measures included the Oswestry Disability Index, the Medical Outcomes Study Short Form-36 and numeric rating scales for back and leg pain, as well as a radiographic assessment of fusion. Outcome measures were evaluated on the basis of the mean change and the percentage of patients reaching a minimum clinically important difference threshold. For comparison, the patients were divided into two groups: 174 patients who were younger than sixty-five years and fifty patients who were sixty-five years of age or older. Results: Substantial improvements from baseline were noted in all of the clinical and health-related quality-of-life measures at the six-month, one-year, and two-year intervals. The mean improvements in the Oswestry Disability Index score at two years postoperatively were 28.5 points for the older patients and 24.5 points for the younger patients. For Short Form-36 physical component summary scores, the mean improvement from baseline was 14.2 points for the older group and 11.7 points for the younger group at two years. The older patients also demonstrated a similar or greater improvement in the numeric rating scale back and leg pain scores at all time intervals, with a significant difference in leg pain scores at two years postoperatively (10.4 points for the older patients and 6.4 points for the younger patients; p = 0.002). Perioperative complications, although an obvious concern, did not appear to adversely affect clinical and health-related quality-of-life outcomes at two years postoperatively. Conclusions: This study demonstrates a substantial benefit for patients sixty-five years of age or older with degenerative disc disease who are treated with a single-level lumbar decompression and instrumented arthrodesis, and we conclude that lumbar arthrodesis is a viable and reasonable treatment option for appropriately selected patients sixty-five years of age or older. Level of Evidence: Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.