The survey interviews approximately 67,500 persons each year. Because of improvements to the survey in 2002, its estimates cannot be compared with those from the 2001 and earlier surveys; the 2002 data thus constitute a new baseline for tracking trends in substance use and other measures. The estimates are presented in terms of lifetime and first-time substance use. The data address illicit drug use, alcohol use, tobacco use, trends in lifetime substance use, trends in the initiation of substance use, youth prevention-related measures, substance dependence or abuse, treatment and treatment need for substance problems, serious mental illness among adults, and treatment for mental health problems. The survey found that in 2002 an estimated 19.5 million Americans (8.3 percent of the population aged 12 or older) were current illicit drug users (used an illicit drug during the month prior to the survey). Marijuana was the most commonly used illicit drug, with a rate of 6.2 percent. An estimated 2.0 million persons (0.9 percent) were current cocaine users, 567,000 of whom used crack. An estimated 6.2 million persons (2.6 percent of the population aged 12 or older) were current users of psychotherapeutic drugs taken nonmedically. An estimated 120 million Americans (51.0 percent of the population aged 12 or older) reported being current drinkers of alcohol, and an estimated 71.5 million Americans (30.4 percent of the population aged 12 or older) reported current use of a tobacco product. The percentage of youths aged 12 to 17 who had ever used marijuana declined slightly from 2001 (21.9 to 20.6 percent). In 2002 an estimated 22.0 million Americans were classified as being substance dependent, and an estimated 3.5 million people aged 12 or older received some kind of treatment for a problem related to the use of alcohol or illicit drugs in the 12 months prior to the survey. In 2002 there were an estimated 17.5 million adults aged 18 or older with serious mental illness, and an estimated 27.3 million adults received mental treatment in the 12 months prior to the interview. 51 figures and 90 tables