Therapeutic alliance (TA) has been associated with therapy effectiveness and treatment outcomes, but findings may differ based upon whether the client or therapist is providing the TA rating. Client-therapist agreement on TA ratings has been associated with symptom change and session smoothness in previous research with adults, and it may also be important in the context of culturally competent care. This study aimed to expand the limited literature by examining client-therapist TA agreement in relationship to youth treatment (YT) engagement in the context of cultural competence. It was hypothesized that youth-therapist TA agreement would be positively related to YT engagement, but that engagement would be better when youths and therapists agreed on higher ratings of TA rather than lower ratings. It was also hypothesized that YT engagement would be better when youth TA ratings were higher than therapist TA ratings. The current study examined the relationship between youth-therapist TA agreement and YT engagement in a culturally diverse sample of 229 outpatient mental health service- using youths aged 12-18 years old and their therapists. Youth and therapists completed separate TA ratings at Time 1 interview, and therapists completed YT engagement ratings at Time 2. Response surface analysis by polynomial regression was used to examine the relationship between youth-therapist TA agreement and YT engagement. The polynomial regression model included five predictor variables and controlled for three service-related variables. Response surface features and test values indicated that the hypotheses were not fully supported. Although the slope along the Line of Agreement suggested that engagement increased as agreement increased, and engagement was better for agreement on high TA ratings compared to low, peak engagement was not along the Line of Agreement. Along the Line of Disagreement, engagement was higher when therapist TA rating was higher than youth TA rating. Findings suggest that TA rating agreement was not the primary driver of YT engagement. Rather, this holistic analytical method provided support for a strong relationship between therapist TA ratings and therapist YT engagement ratings. Future research may examine different ways of analyzing youth-therapist TA agreement and its relationship to treatment engagement and other outcomes.