Abstract BACKGROUND: The safety and efficacy of spinal fusion in the elderly population remains uncertain with conflicting data. OBJECTIVE: To determine if elderly patients undergoing instrumented lumbar fusion have increased 30-day complication rates compared to younger patients. METHODS: The American College of Surgeons National Surgical Quality Improvement Program was used to identify all patients undergoing instrumented posterolateral lumbar fusion between 2005 and 2011. Patients were stratified by decade cohorts as follows: <65, 65 to 75, 75 to 85, and ≥85 years old. All 30-day complications were grouped as overall composite morbidity and were compared using multivariate analysis. RESULTS: A total of 1395 patients were identified and the overall 30-day complication rate was 11.47%. The complication rates were 9.04% and 14.05% for patients younger than 65 and older than 65, respectively. When stratified by decade cohorts, the complication rates were 9.04% for the <65 cohort, 13.46% for the 65 to 75 cohort, 16.17% for the >75 to 85 cohort, and 4.00% for the ≥85 cohort. Multivariable regression analysis revealed no statistically significant difference between the <65 and ≥65 age cohorts (odds ratio = 1.26; 95% confidence interval: 0.87-2.19). After stratifying into age cohorts, multivariable analyses revealed no difference in odds of postoperative complication occurrence for any age cohort when compared with the referent group (<65 years of age). CONCLUSION: Patients older than 65 years of age have significantly higher rates of complications after lumbar fusion when compared to younger patients. However, multivariable analysis revealed that age was not an independent risk factor for complication occurrence after lumbar fusion.