Objectives: Insurance status has been shown to impact survival outcomes. We sought to determine whether insurance affects the choice of treatment modality among patients with advanced (T4) oral cavity squamous cell carcinoma (OCSCC). Design: Retrospective, population-based cohort study Setting: The Survival, Epidemiology, and End Results (SEER) Program database Participants: The population included all adult (age > 18) patients with advanced (T4a or T4b) OCSCC diagnosed from 2007 to 2016. Main outcome measures: The main outcome measure was the odds of receiving definitive treatment, defined as primary surgical resection. Insurance status was categorized into uninsured, any Medicaid, and insured groups. Univariable, multivariable, and subgroup analyses were performed. Results: The study population consisted of 2628 patients, of whom 1915 (72.9%) were insured, 561 (21.3%) had Medicaid, and 152 (5.8%) were uninsured. The multivariable model showed that patients who were 80 years or older, unmarried, with T4b disease, received treatment in the pre-Affordable Care Act (ACA) period, and who were on Medicaid or uninsured were significantly less likely to receive definitive treatment. Among patients with T4a disease, insured patients were significantly more likely to receive definitive treatment compared to those on Medicaid or uninsured (OR=0.69, 95% CI 0.54-0.88, p<0.0001 [Medicaid vs. Insured]; and OR=0.65, 95% CI 0.43-0.98, p=0.001 [Uninsured vs. Insured]), however these differences did not persist when considering only those patients treated following the 2014 expansion of the ACA. Conclusions: Insurance status is significantly associated with treatment modality among adults with advanced stage (T4a) OCSCC. These findings support the premise of expanding insurance coverage in the United States.