That Medicare is universal for seniors is widely accepted by leading analysts. But in the context of developing detailed policies that seek to cover as many people as possible, it is inaccurate to make Medicare eligibility sound so simple and inclusive. To estimate the number of seniors without full federal Medicare Part A coverage, we examined data for uninsured seniors, seniors with Medicaid and no Medicare coverage of any kind, seniors with Medicare Part B but without Part A, and seniors bought into Part A by their state Medicaid programs. We found that in 2005, 1.6 million seniors—or 5 percent of the elderly U.S. population—were without a full federal Part A premium subsidy. The share of seniors without this benefit was notably higher in the nation's two largest states—California (12 percent) and New York (8 percent). We estimate that reforming Medicare Part A to make the benefit truly universal and fully federal would cost the federal government $6 billion in new spending in federal fiscal year 2011, an increase in baseline federal Medicare expenditures of 1.1 percent.