This study examined group leaders' adherence to The Incredible Years Parenting Program's components and collaborative process during a yearlong dissemination in a large multicultural city and universal prevention context. Mixed methods were used to evaluate adherence and develop an understanding of the barriers and facilitators of therapist fidelity. Results suggest that the protocol and collaborative group processes were implemented with a high degree of adherence with the three exceptions of role plays, videotape modeling dosage, and "buddy calls." A number of interconnected barriers with implications for future implementation were identified. Key contributors to adherence included the training and structure of the program, emphasis on accountability and ongoing session monitoring, and important aspects of supervision and group leader qualities. (Contains 1 table.)