Objective: Aspects of depressed adolescents' perceived interpersonal functioning were examined as moderators of response to treatment among adolescents treated with interpersonal psychotherapy for depressed adolescents (IPT-A; Mufson, Dorta, Moreau, & Weissman, 2004) or treatment as usual (TAU) in school-based health clinics. Method: Sixty-three adolescents (12-18 years of age) participated in a clinical trial examining the effectiveness of IPT-A (Mufson, Dorta, Wickramaratne, et al., 2004). The sample was 84.1% female and 15.9% male (mean age = 14.67 years). Adolescents were 74.6% Latino, 14.3% African American, 1.6% Asian American, and 9.5% other. They came primarily from low-income families. Adolescents were randomly assigned to receive IPT-A or TAU delivered by school-based mental health clinicians. Assessments, completed at baseline and at Weeks 4, 8, and 12 (or at early termination), included the Hamilton Rating Scale for Depression (Hamilton, 1967), the Conflict Behavior Questionnaire (Robin & Foster, 1989), and the Social Adjustment Scale-Self-Report (Weissman & Bothwell, 1976). Results: Multilevel modeling indicated that treatment condition interacted with adolescents' baseline reports of conflict with their mothers and social dysfunction with friends to predict the trajectory of adolescents' depressive symptoms over the course of treatment, controlling for baseline levels of depression. The benefits of IPT-A over TAU were particularly strong for the adolescents who reported high levels of conflict with their mothers and social dysfunction with friends. Conclusions: Replication with larger samples would suggest that IPT-A may be particularly helpful for depressed adolescents who are reporting high levels of conflict with their mothers or interpersonal difficulties with friends. (Contains 6 tables, 4 figures and 1 footnote.)