April 18, 2005 National Expenditures for Mental Health Services and Substance Abuse Treatment 1991-2001  An estimated 28 to 30 percent of the adult U.S. population will suffer from a mental or substance use disorder during the course of a year. In any given year, about five to seven percent of adults have a serious mental illness (Kessler et al., 2001). A similar percentage of children-about five to nine percent-has a serious emotional disturbance (Friedman et al., 1996). Of the ten leading causes of disability worldwide in 2000 among individuals age 15 to 44, five were . . .