The Social Security Administration (SSA) administers two programs that provide benefits based on disability: the Social Security Disability Insurance (SSDI) program and the Supplemental Security Income (SSI) program. The SSDI program provides disability benefits to people who are under the full retirement age and are no longer able to work because of a disabling medical condition or because they have a terminal illness. The SSI program is a means-tested income-assistance program for disabled, blind, and aged people who have limited income and resources regardless of their prior participation in the labor force. SSA asked the National Academies to conduct a study of health-care utilizations by adults being evaluated for disability determination. It provides an analysis of health-care utilizations as they relate to impairment severity and SSA’s definition of disability. The committee identified types of utilizations that might be good proxies for listing-level severity, that is, what represents an impairment, or combination of impairments, severe enough to prevent a person from doing any gainful activity regardless of age, education, or work experience.