A national probability sample of households was selected from 100 primary sampling units, including more than 98 percent of the U.S. population. Persons living in group quarters or institution and transient populations were excluded, along with residents of Alaska and Hawaii. Methods included interviewing and questionnaires. Age and race/ethnicity were the two primary correlates of drug use on which the 1988 sample was stratified. Estimates of the percentage or number of persons illicitly using drugs, or a particular drug, are provided. Data for the prevalence of the individual illicit drugs, licit drugs, and psychotherapeutic drugs are presented. Illicit drugs included marijuana, cocaine, crack, inhalants, and hallucinogens. Psychotherapeutic drugs include stimulants, sedatives, tranquilizers, and analgesics. The prevalence of PCP use, heroin use, and the use of needles with heroin, cocaine, or amphetamines is also presented. The estimates produced should be viewed as approximations based on the best data available at this time. 6 footnotes, 21 tables.