Brief addiction treatments, including motivational interviewing (MI), have shown promise with youth. One underexamined factor in this equation is the role of therapist behaviors. We therefore sought to assess whether and how therapist behaviors differ for Hispanic versus non-Hispanic youth and how that may be related to treatment outcome. With 80 substance-using adolescents (M age = 16 years; 65% male; 59% Hispanic; 41% non-Hispanic), we examined the relationship between youth ethnicity and therapist behaviors across two brief treatments (MI and alcohol/marijuana education [AME]). We then explored relationships to youth 3-month treatment response across four target outcomes: binge drinking days, alcohol-related problems, marijuana use days, and marijuana-related problems. In this study, therapists showed significantly more MI skills within the MI condition and more didactic skills in the AME condition. With respect to youth ethnicity, across both conditions (MI and AME), therapists used less MI skills with Hispanic youth. Contrary to expectations, therapists' use of MI skills was not connected to poorer outcomes for Hispanic youth across the board (e.g., for binge drinking days, marijuana use days, or marijuana-related problems). Rather, for Hispanic youth, therapists' use of lower MI skills was related only to poorer treatment outcomes in the context of alcohol-related problems. The observed relationships highlight the importance of investigating salient treatment interactions between therapist factors and youth ethnicity to guide improvements in youth treatment response.