Meeting the health care needs of millions of elderly and disabled Americans is central to the debate over Medicare's future. Using data from a nationally representative survey of 3,309 beneficiaries, Medicare's most vulnerable beneficiaries were profiled, examining variations in coverage, satisfaction, access, and financial difficulties. A substantial portion of the Medicare population--two thirds--were found to have health problems or low incomes. The analysis found that about 40% of beneficiaries with incomes below the poverty level, in fair or poor health, or with ADL limitations, have difficulties paying their medical bills or getting needed health care. Medicare's disabled, under-65 beneficiaries are at even higher risk: nearly half (47%) have health care access problems or deal with financial hardship due to medical bills. The diverse needs and experiences of the Medicare population are underscored, providing new insights into the challenge of maintaining or improving protection for those with greatest need while assuring the long-term fiscal viability of the program.