Objectives: The present study presents background and pretreatment characteristics of adolescent substance abuse treatment clients, and it provides a mechanism for describing perhaps the largest research sample of adolescents who were in drug treatment in this decade. Methods: The sample was 3382 subjects who presented for treatment from 1993 to 1995 in 37 programs in Pittsburgh, Pennsylvania; Miami, Florida; Minneapolis, Minnesota; Chicago, Illinois; Portland, Maine; and New York City, New York. Informed permission for the youth to participate was obtained from the subject's custodial parent/guardian, and both the youth and the youth's parents or guardians provided informed assent if they agreed to participate as subjects. Adolescents then were interviewed privately and confidentially by a trained professional interviewer who was independent of the treatment programs. The interviews queried subjects about their background, including education and employment; physical and mental health; use of tobacco, alcohol, and other drugs; sexual experiences; legal problems; religious beliefs; and treatment experience. Results: The long-term residential treatment modality was the least gender balanced of the modalities and had the most African-American and Hispanic clients. This modality was distinguished by the proportion of clients who were referred to treatment by the juvenile or criminal justice system. Compared with other clients in other modalities, short-term inpatient clients were more likely to be female and white. Inpatient clients also reported more indicators of psychiatric impairment. Outpatient clients were slightly younger than clients in the other modalities, and more of them were attending school at the time of admission to treatment. Outpatient clients had the least criminally involved lifestyles, their rates of (regular daily or weekly) drug use were also the lowest of the three modalities for all drugs assessed, and they had the least drug treatment experience. Conclusions: These results merit several recommendations. One is the need for more community-based adolescent substance abuse treatment programs. An additional recommendation is for more substance abuse treatment programs in facilities that serve incarcerated youth. Finally, and perhaps most critically, it is recommended that programs be designed to address such specialized issues as comorbid substance abuse and psychiatric problems, family dysfunction, physical and sexual abuse, gender and ethnic differences, and academic performance.