The authors investigated changes in treatment team functioning in an adult inpatient psychiatric hospital after the implementation of a mindfulness-based mentoring intervention. Using a multiple baseline across treatment teams design, the authors assessed levels of functioning of three treatment teams using a 50-item rating scale and then introduced mindfulness-based mentoring successively across the treatment teams. Following intervention, four follow-up assessments at 3-month intervals were undertaken to assess the durability of the enhanced treatment team functioning levels in the absence of mentoring. Results showed that with the introduction of mindfulness-based mentoring, treatment team performance was enhanced, patients' attendance at therapeutic groups and individual therapy sessions was maximized, and patient and staff satisfaction with treatment team functioning was substantially increased, with patient satisfaction showing greater gains than staff satisfaction. Mindfulness-based mentoring may be an efficient and effective intervention for enhancing and maintaining the performance of treatment teams in adult psychiatric hospitals. (Contains 2 tables and 2 figures.)