Objective: The Treatment for Adolescents With Depression Study is a multicenter, randomized clinical trial sponsored by the NIMH. This study is designed to evaluate the short- and long-term effectiveness of four treatments for adolescents with major depressive disorder: fluoxetine, cognitive-behavioral therapy, their combination, and, acutely, pill placebo. This report describes the demographic and clinical characteristics of the sample and addresses external validity. Method: Participants are 439 adolescents, aged 12-17 years inclusively, with a primary DSM-IV diagnosis of current major depressive disorder. Baseline data are summarized and compared with those from national samples and previous trials. Results: The sample composition is 54.4% girls, 73.8% white, 12.5% African American, and 8.9% Hispanic. The mean Child Depression Rating Scale-Revised total score is 60.1 (SD = 10.4, range 45-98) with 86.0% experiencing their first major depressive episode. The most common concurrent diagnoses are generalized anxiety disorder (15.3%), attention-deficit/hyperactivity disorder (13.7%), oppositional defiant disorder (13.2%), social phobia (10.7%), and dysthymia (10.5%). Demographic results are consistent with data from national samples and large psychopharmacology trials involving depressed adolescents. Conclusions: The Treatment for Adolescents With Depression Study provides a large, diverse, and representative sample of depressed adolescents that highlights the complexity of major depressive disorder in adolescents and provides a rich source for explicating the effects of moderator and mediator variables on baseline psychopathology and treatment outcome.