The absence of health insurance coverage has been associated with worse outcomes for patients with metastatic renal cell carcinoma (mRCC). Medicaid expansion in the United States was an important provision of the Affordable Care Act, which increased the number of low-income individuals eligible for Medicaid starting in January 2014 in several states. The effect of Medicaid expansion on access to healthcare for patients with mRCC is unknown. We performed a retrospective cohort study of 6844 patients aged < 65 years with mRCC at diagnosis within the National Cancer Database. We compared the time to treatment and the rates of no insurance before (2012-2013) and after (2015-2016) expansion between patients living in states that had and had not expanded Medicaid using difference-in-difference (DID) analyses. DIDs were calculated using linear regression analysis with adjustment for sociodemographic covariates. The rate of no insurance did not change in the expansion states compared with the nonexpansion states (DID, −0.55%; 95% confidence interval, −3.32% to 2.21%; P = .7). The percentage of patients receiving treatment within 60 days of diagnosis had increased in the expansion states from 43% to 49% and in the nonexpansion states from 42% to 46% after expansion. No change was found in treatment within 60 days of diagnosis among all patients (DID, 2.81%; 95% confidence interval, −2.61% to 8.22%; P = .3). Medicaid expansion was not associated with improved healthcare access for patients with mRCC as reflected by timely treatment. Future work should assess the association between Medicaid expansion and oncologic outcomes. We assessed whether Medicaid expansion has led to more timely treatment of metastatic renal cell carcinoma (mRCC). We compared the time to treatment before and after expansion between the states that had and had not expanded Medicaid for patients with mRCC within the National Cancer Database. Medicaid expansion was not associated with more timely treatment for patients with mRCC.