Although a growing literature has focused on the impact of cash benefits of Social Security Disability Insurance (SSDI), beneficiaries also eventually gain coverage by Medicare, one of the few under-65 groups eligible for Medicare. This healthcare coverage has significant value given the limited alternatives available to the people with long-term disabling conditions; however, original Medicare carries with it substantial cost-sharing and premiums (Part B premiums amount to over 10% of the average monthly SSDI benefit), and, the under-65 Medicare population have limited options for supplemental coverage. Dual eligibility with Medicaid has been a source of this supplemental coverage for the population of people with disabilities, but, traditionally, only for those who could satisfy Medicaid’s asset and income tests. Recent Medicaid expansions therefore provided the option of supplemental coverage to a broader swathe of the under-65 Medicare population if these beneficiaries happened to live in the states that expanded Medicaid. This proposed research estimates the impact of this supplemental coverage on the economic security, health care utilization, and health of SSDI beneficiaries. Our analytic approach will leverage both the between-state differences in which states expanded Medicaid as well as the within-state differences in which SSDI beneficiaries would be affected by this expansion and which would not (e.g., those already covered by Medicaid).