Purpose: The aim of this study was to design and trial an Adherence Scale to measure fidelity of Motivational Care Planning (MCP) within a clinical trial. This culturally adapted therapy MCP uses a client centered holistic approach that emphasises family and culture to motivate healthy life style changes. Methods: The Motivational Care Planning-Adherence Scale (MCP-AS) was developed through consultation with Aboriginal and Islander Mental Health Initiative (AIMhi) Indigenous and non-Indigenous trainers, and review of MCP training resources. The resultant ten-item scale incorporates a 9-Point Likert Scale with a supporting protocol manual and uses objective, behaviourally anchored criteria for each scale point. A fidelity assessor piloted the tool through analysis of four audio-recordings of MCP (conducted by Indigenous researchers within a study in remote communities in Northern Australia). File audits of the remote therapy sessions were utilised as an additional source of information. A Gold Standard Motivational Care Planning training video was also assessed using the MCP-AS. Results: The Motivational Care Planning-Adherence Scale contains items measuring both process and content of therapy sessions. This scale was used successfully to assess therapy through observation of audio or video-recorded sessions and review of clinical notes. Treatment fidelity measured by the MCP-AS within the pilot study indicated high fidelity ratings. Ratings were high across the three domains of rapport, motivation, and self-management with especially high ratings for positive feedback and engagement, review of stressors and goal setting. Conclusions: The Motivational Care Planning-Adherence Scale has the potential to provide a measure of quality of delivery of Motivation Care Planning. The pilot findings suggest that despite challenges within the remote Indigenous community setting, Indigenous therapists delivered therapy that was of high fidelity. While developed as a research tool, the scale has the potential to support fidelity of delivery of Motivation Care Planning in clinical, supervision and training settings. Larger studies are needed to establish inter-rater reliability and internal and external validity.