The present study describes the development of the Mindfulness-Based Relapse Prevention Adherence and Competence Scale (MBRP-AC), a measure of treatment integrity for mindfulness-based relapse prevention (MBRP). MBRP is a newly developed treatment integrating core aspects of relapse prevention with mindfulness practices. The MBRP-AC was developed in the context of a randomized controlled trial (RCT) of MBRP efficacy and consists of two sections: Adherence (adherence to individual components of MBRP and discussion of key concepts) and Competence (ratings of therapist style/approach and performance). Audio recordings from 44 randomly selected group treatment sessions (50%) were rated by independent raters for therapist adherence and competence in the RCT. Findings evinced high interrater reliability for all treatment adherence and competence ratings, and adequate internal consistency for Therapist Style/Approach and Therapist Performance summary scales. Ratings on the MBRP-AC suggested that therapists in the recent RCT adhered to protocol, discussed key concepts in each session, and demonstrated the intended style and competence in treatment delivery. Finally, overall ratings on the Adherence section were positively related to changes in mindfulness over the course of the treatment.