PROJECT SUMMARY/ABSTRACT Approximately 12 million low-income Medicare beneficiaries are dually enrolled in Medicaid, which pays for services not covered by Medicare and defrays out-of-pocket costs, which can be substantial for relatively poor people. Medicare’s premiums, deductibles, and coinsurance average over 40% of an individual’s Social Security income, which represents the sole source or majority of income for many low-income Medicare beneficiaries. Medicaid coverage enables low-income Medicare beneficiaries to afford care they might otherwise forego due to cost. However, poor coordination between Medicare and Medicaid, complex Medicaid eligibility and enrollment rules, and state variation in Medicaid rules create substantial differences in who is eligible for and receives Medicaid. This proposal focuses on how variation in state Medicaid policy affects Medicaid enrollment, cost-related barriers to care, and heath care utilization in low-income aging and disabled populations. The proposed study will use recent Medicaid policy changes in Indiana and Ohio as a natural experiment to assess how increasing eligibility and simplifying enrollment impacted the low-income Medicare population. Data from the American Community Survey, Behavioral Risk Factor Surveillance System, and Medicare claims will be used to address the specific aims of this research. Aim 1 will estimate changes in Medicaid enrollment following eligibility expansions for low-income Medicare beneficiaries. Enrollment in Medicaid lowers out-of- pocket cost sharing requirements and facilitates care seeking. Therefore, Aim 2 will examine how access to care was affected by changes in Medicaid eligibility for low-income Medicare beneficiaries. Increases in health care utilization are expected for services where Medicare’s cost-sharing requirements are reduced or eliminated by Medicaid, and for services that may be sensitive to deferred preventive care use. Aim 3 will analyze changes in healthcare utilization after Medicaid eligibility expanded for low-income Medicare beneficiaries. Difference-in-differences and event study models will be utilized. The proposed project’s aims align with the Agency for Healthcare Research and Quality’s (AHRQ) mission “to produce evidence to make health care safer, higher quality, more accessible, equitable, and affordable,” and a Healthy People 2020 goal to improve access to care. Additionally, three AHRQ Priority Populations, the elderly, low-income, and those with special healthcare needs are the focus of the proposal. Findings from this proposal can inform future policy, research, and programs to promote access to care in low-income, aging, and disabled populations.