By the time they enter the Medicare program at age 65, uninsured older adults—particularly those with chronic conditions—often have health problems that require more intensive and costly care than if these individuals had been continuously insured. This proposed two-phase project will inform policymakers about the potential health gains of expanding Medicare coverage to older adults under 65, and how the cost of such an expansion could be offset by savings to the Medicare program. Using Medicare claims data and findings from the longitudinal Health and Retirement Study, project staff in the first phase will assess the impact that gaining Medicare coverage has on health care use and out-of-pocket costs for previously uninsured adults and other disadvantaged, near-elderly adults, as well as the impact on Medicare program costs. If this work proceeds satisfactorily, a second phase would be proposed to assess how Medicare affects health, mortality, and care of chronic conditions within this population.