This study describes a multimethod evaluation of treatment fidelity to the family therapy (FT) approach demonstrated by front-line therapists in a community behavioral health clinic that utilized FT as its routine standard of care. Study cases (N=50) were adolescents with conduct and/or substance use problems randomly assigned to routine family therapy (RFT) or to a treatment-as-usual clinic not aligned with the FT approach (TAU). Observational analyses showed that RFT therapists consistently achieved a level of adherence to core FT techniques comparable to the adherence benchmark established during an efficacy trial of a research-based FT. Analyses of therapist-report measures found that compared to TAU, RFT demonstrated strong adherence to FT and differentiation from three other evidence-based practices: cognitive-behavioral therapy, motivational interviewing, and drug counseling. Implications for rigorous fidelity assessments of evidence-based practices in usual care settings are discussed.