This study examined relations between therapist, caregiver, and youth characteristics and therapist adherence to multisystemic therapy (MST). Participants were 405 therapists in 45 organizations and the 1,711 families they treated with MST. Therapist perceptions that the flexible hours required to implement MST are problematic predicted lower adherence. Therapist demographic variables, professional training and experience, endorsement of the MST model, perceived difficulty and rewards of doing MST, and perceived similarity to treatments previously used did not predict adherence. Therapist-caregiver similarity on ethnicity and gender predicted higher adherence. Low caregiver education and African American ethnicity predicted higher adherence. With the exception of youth psychosocial functioning, indicators of severity of youth problems did not predict adherence.