In a continuation of long-term trends, life expectancy has been steadily increasing in the United States for the past several decades. Accompanying the recent increases, however, is a growing disparity in life expectancy between individuals with high and low income and between those with more and less education. The difference in life expectancy across socioeconomic groups is significantly larger now than in 1980 or 1990. A similar trend is evident in Great Britain but not in Canada, where the gap in life expectancy between high- and low-income individuals has declined. Increasing longevity, by itself, has clear implications for Social Security and Medicare expenditures. As beneficiaries live longer, they will receive benefits for a longer period, putting additional pressure on the programs' finances. The implications of a continued widening of the gap in life expectancy by socioeconomic status are clear for Social Security but less so for Medicare. For Social Security, a widening gap would worsen the long-term shortfall in financing and reduce the program's progressivity--the extent to which it redistributes resources from high-income to low-income beneficiaries on a lifetime basis. For Medicare, it is not clear whether a widening gap would exacerbate the cost increases that will result from increasing longevity. How the share of Medicare spending on low-income individuals would change depends on how the percentage change in life expectancy at age 65 compares for the various groups of beneficiaries. (Contains 2 figures and 21 footnotes.)