The development of the Mindfulness-Based Cognitive Therapy Adherence Scale (MBCT-AS) is described. This 17-item scale measures therapist adherence to the treatment protocol for Mindfulness-Based Cognitive Therapy (MBCT), a treatment for the prevention of recurrence in Major Depressive Disorder. The MBCT-AS assesses therapist behaviours specific to (MBCT) as well as therapy practices that MBCT shares with Cognitive Behaviour Therapy (CBT). To determine the utility of this scale, we compared delivery of group MBCT against group CBT, with independent ratings of taped sessions provided to measure adherence to MBCT and CBT for therapists in both groups. The results showed that: (a) raters can reliably use the MBCT-AS; (b) MBCT therapists demonstrated adherence to the treatment protocol, as measured by the MBCT-AS; and (c) MBCT is distinguishable from CBT on both the MBCT-AS and a scale measuring adherence to CBT (CBT-AS). These findings indicate that the MBCT-AS may be a useful tool for ensuring the proper delivery of MBCT in future research, and may be helpful in determining the elements of MBCT that are unique to that treatment. Copyright © 2002 John Wiley & Sons, Ltd.