This study examined interpersonal predictors of early therapeutic alliance in a cognitive-behavioral treatment study for adolescents with anxiety and/or depressive disorders. Client, therapist, and observer rated measures of alliance were obtained from the third session of treatment in a sample of twenty-seven adolescents. Results indicate that alliance ratings across the three perspectives are significantly associated with one another, but that pretreatment interpersonal variables were differentially associated with varying informant perspectives. Adolescents’ perceptions of their relationships to their caregivers positively related to their perceptions of the therapeutic alliance, such that adolescents with more positive representations of relationships with their attachment figures were more likely to endorse stronger working alliances early in treatment. Adolescent-reported symptom severity at pretreatment predicted observer ratings of alliance, such that adolescents who indicated greater symptoms at pretreatment were rated as having stronger early alliances with their therapists by independent observers. Adolescent perceptions of social support also predicted observer ratings of alliance. Therapists perceived having weaker alliances with adolescents showing clinically significant depression, as compared to adolescents diagnosed with anxiety disorders alone. Future research is needed to examine whether identification of relevant interpersonal factors can help improve therapeutic engagement and outcomes for the psychosocial treatment of adolescents with anxiety and depressive disorders.