Client-therapist consensus has been hypothesized to be an important element of culturally competent care. However, little is known about the relationship between explanatory model agreement and treatment engagement, particularly for services involving adolescents, where both parent and youth perspectives may need to be considered. This longitudinal study collected youth, parent, and therapist survey data on etiological beliefs as well as therapist-rated treatment engagement related to a culturally diverse sample of 285 outpatient mental health service-using youth (aged 12-18, M = 14.06 at Time 1 interview; 40% female). Youth-therapist and parent-therapist agreement on beliefs about the etiology of the youth's mental health problems were examined in relationship to later treatment engagement. Although parent-therapist agreement was unrelated to parent engagement, youth-therapist coendorsement of etiological beliefs predicted overall youth treatment engagement. In addition, youth-therapist agreement significantly predicted specific aspects of youth engagement: client-therapist interaction, communication/openness, and client's perceived usefulness of treatment. Results speak to the importance of agreement between therapist and youth upon key issues related to the youth's problems in mental health treatment settings and support facilitation of consensus as a component of culturally competent care. Differences between findings for youth and parents suggest that therapeutic relationships may vary for different stakeholders, indicating a need to consider individual perspectives and contributions separately.