Adolescents entering treatment for alcohol and drug problems are typically experiencing some type of crisis, and families have often exhausted their resources for managing the behavior of teenagers. While adolescent treatment programs have rapidly developed over the past decade, clinical characteristics of adolescents following drug abuse treatment have not been adequately studied and the arena of clinical outcome research has only begun to appreciate the complexities involved in the clinical course of adolescent drug abuse. Adolescent alcohol and drug involvement patterns vary markedly from those of adults, and teenagers face many formidable developmental tasks, in addition to establishing major lifestyle changes in the posttreatment recovery period. Although adolescent alcohol and drug treatment programs have produced some success, there is also considerable relapse following treatment. Significant improvement can be attained in major areas of adolescent functioning with only 1 year of abstinence, but measurable deterioration in functioning continues when adolescents revert to drug abuse in the year following treatment. While posttreatment factors appear to significantly influence the clinical course of adolescent drug abuse, the heterogeneity of the population and pathways to improved functioning after treatment may vary. Clearly, additional research is needed to determine prognostic indicators of long-term course, particularly as adolescents move through young adulthood which is the highest risk period for alcohol and drug abuse. 40 references, 3 tables, and 2 figures