Data on use of psychotherapeutic drugs were obtained in personal interviews with a cross-section sample of adults in San Francisco. Proportions using such drugs during the year prior to interview were 45% for women and 33% for men. Prevalence of use, however, varies greatly by sex and age of person, by therapeutic class, and by intended and actual source of drug. Persons between 45 and 59 are more likely than others to use prescription drugs from medical sources. Use of over-the-counter drugs and prescription drugs obtained from nonmedical sources is most prevalent among persons 18 to 29. Overall, prevalence of psychotherapeutic drug use is highest among persons under 30. Persons who obtain prescription drugs from nonmedical sources are more likely than others to use a variety of drugs, but are less likely to use any drug regularly.