Prevalence, Most Common Causes of Disability Among Adults in the US, 2005

From the Morbidity and Mortality Weekly Report (CDC):

This analysis determined that the estimated percentage of U.S. adults reporting a disability has not changed since 1999, when, using the same survey and definitions, 22.0% of adults reported having a disability. Reasons for this leveling off likely include a better educated public, improved medical interventions, increased public health attention to behavior modifications (e.g., tobacco use), and increased access to assistive technology among the most advantaged socioeconomic groups.

Although the percentage has not changed, this analysis and other studies have determined that the absolute number of persons in the U.S. population reporting disabilities is increasing because of a rise in the at-risk population.