In this study we compare the beneficiaries with various types of Medicare supplemental insurance coverage to examine the impact of socioeconomic characteristics on such coverage. We found that those who are more disadvantaged are less likely to have any coverage, and those who have it are less likely to have it subsidized by a former employer. These findings have direct implications for the fairness of proposed programs to provide prescription drug coverage to Medicare beneficiaries, and for the advisability of various proposals for reforming Medicare, including "premium-support" programs.