Objectives. This study assessed the effects of reducing fatal and nonfatal health conditions on the number of functionally limited older Americans in the coming decades. Methods. Data from the 1990 census and the Longitudinal Study of Aging were used to project the number of functionally limited older Americans from 2001 to 2049, assuming 1% biennial reductions in five conditions that shorten life expectancy (coronary artery disease, stroke, cancer, diabetes, and confusion) and one condition that decreases functional ability (arthritis). Results. Decreasing the prevalence of arthritis by 1% every 2 years would lead to a much greater reduction in functional limitation between 2001 and 2049 (4 million person-years) than would decreasing any of the other conditions by the same amount. Decreases in two fatal conditions (cancer and coronary artery disease) would lead to increases in functional limitation (0.9 and 0.1 million person-years, respectively). Conclusions. Advances against common nonfatal disabling conditions would be more effective than advances against fatal conditions in blunting the large increase in the functionally limited older population anticipated in the 21st century.