BACKGROUND: The SPORT (Spine Patient Outcomes Research Trial) reported favorable surgery outcomes over 2 years among patients with stenosis with and without degenerative spondylolisthesis, but the economic value of these surgeries is uncertain. OBJECTIVE: To assess the short-term cost-effectiveness of spine surgery relative to nonoperative care for stenosis alone and for stenosis with spondylolisthesis. DESIGN: Prospective cohort study. DATA SOURCES: Resource utilization, productivity, and EuroQol EQ-5D score measured at 6 weeks and at 3, 6, 12, and 24 months after treatment among SPORT participants. TARGET POPULATION: Patients with image-confirmed spinal stenosis, with and without degenerative spondylolisthesis. Time Horizon: 2 years. PERSPECTIVE: Societal. INTERVENTION: Nonoperative care or surgery (primarily decompressive laminectomy for stenosis and decompressive laminectomy with fusion for stenosis associated with degenerative spondylolisthesis). OUTCOME MEASURES: Cost per quality-adjusted life-year (QALY) gained. RESULTS OF BASE-CASE ANALYSIS: Among 634 patients with stenosis, 394 (62%) had surgery, most often decompressive laminectomy (320 of 394 [81%]). Stenosis surgeries improved health to a greater extent than nonoperative care (QALY gain, 0.17 [95% CI, 0.12 to 0.22]) at a cost of $77,600 (CI, $49,600 to $120,000) per QALY gained. Among 601 patients with degenerative spondylolisthesis, 368 (61%) had surgery, most including fusion (344 of 368 [93%]) and most with instrumentation (269 of 344 [78%]). Degenerative spondylolisthesis surgeries significantly improved health versus nonoperative care (QALY gain, 0.23 [CI, 0.19 to 0.27]), at a cost of $115,600 (CI, $90,800 to $144,900) per QALY gained. RESULT OF SENSITIVITY ANALYSIS: Surgery cost markedly affected the value of surgery. LIMITATION: The study used self-reported utilization data, 2-year time horizon, and as-treated analysis to address treatment nonadherence among randomly assigned participants. CONCLUSION: The economic value of spinal stenosis surgery at 2 years compares favorably with many health interventions. Degenerative spondylolisthesis surgery is not highly cost-effective over 2 years but could show value over a longer time horizon.