An estimated 13 percent of adolescents ages 12-17 had emotional problems as indicated by withdrawal, somatic problems, anxiety, and depression. An estimated 17 percent of adolescents aged 12-17 had behavioral problems as indicated by delinquent or aggressive behavior. The likelihood of substance use among adolescents was associated with the severity of emotional and behavioral problems across age and gender groups. Nine percent of the youths reported use of illicit drugs in the past month, including 7 percent who reported past-month use of marijuana and 4 percent who reported past-month use of illicit drugs other than marijuana. Past-month marijuana use was nearly twice as likely and use of other illicit drugs as four times more likely for adolescents with serious emotional problems than for youths with low levels of emotional problems. Marijuana use was even more likely for youths with serious behavioral problems than for other youths. Twenty-percent of youths reported using alcohol in the past month. Past month alcohol use was nearly twice as likely for adolescents with serious emotional problems and nearly three times as likely for youths with serious behavior problems than for other youths. Adolescents with serious emotional or behavioral problems were also several times more likely to be dependent on alcohol or illicit drugs than were other adolescents. Tables, appended methodological information and tables, and 86 references