Abstract Background: People who smoke have a higher risk of developing cancer and disproportionately lower incomes which worsens healthcare access and health outcomes. The Affordable Care Act expanded Medicaid eligibility to adults with income up to 138% of the federal poverty line. It is unknown if and how Medicaid expansions changed healthcare access, preventive service use, and health behaviors. Also, it is unknown whether expansions impacted income or racial/ethnic disparities in these measures, given historically lower healthcare access and utilization in lower income people and people of color. Methods: Data were from the nationally representative Behavioral Risk Factor Surveillance System surveys between 2011-2019 of adults ages 18-64 years who currently smoked cigarettes and former smokers who had quit in the past year (n=580,858). Generalized difference-in-differences (DID) analyses using logistic regression models examined the association of Medicaid expansions (staggered time-varying exposure, 34 states expanded as of December 2019) with healthcare access (insurance coverage, care affordability, usual source of care), preventive service use (routine checkup, flu shot, HIV test, breast and colorectal cancer screening, cholesterol check, dentist visit), and health/risk behaviors (heavy alcohol drinking, obesity), including cessation behaviors (past-year quit attempt, successful cessation for >3 months). Income and race/ethnicity differences were also tested. Results: Among people who smoke, Medicaid expansions were associated with healthcare access and preventive care utilization improvements, but not health behaviors, including cessation. Expansions resulted in narrowing of disparities in several measures across income levels and Black vs. White people in expansion states. For example, expansion associated gains in insurance coverage were significantly larger in low-income (expansion: 74.6% vs. nonexpansion: 60.8%; DID: 13.8% 95% CI: 12.8, 14.8%) than high-income (insurance: 87.5% vs. 93.7%, DID: -6.2% points 95% CI: -7.2, -5.2%); and in Black people (82.6% vs. 74.6%, DID: 7.9% points 95% CI: 6.3, 9.5%) than White people (79.5% vs. 75.7%; DID: 3.8%, 95% CI: 3, 4.6%). Medicaid expansions gains were also larger among lower than higher income people for all in preventive care utilization measures studied; and uptake of flu shots, mammograms, and HIV tests were larger in Black than White people. Significant gains in multiple measures were also observed for Hispanic and American Indian/Alaska Native people who smoke, but changes were generally no different than White people. Conclusions: Among people who smoke, Medicaid expansions improved healthcare access and preventive services use. Expansions were also associated with a reduction, but not elimination, of income and Black-White disparities in healthcare access and utilization. Despite insurance and preventive service gains, expansions were not associated with cessation behaviors, signaling the need for improving comprehensive cessation treatments in Medicaid expansion programs. Citation Format: Priti Bandi, Samuel Asare, J. Lee Westmaas, Nigar Nargis, Robin Yabroff, Ahmedin Jemal, Xuesong Han, Stacey Fedewa. Association of Affordable Care Act Medicaid expansions with healthcare access and utilization among people who smoke [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PR-01.