Background: While Motivational Interviewing (MI) is effective in reducing client problem behaviours, including health-related behaviours, there is little evidence about how MI training enhances practitioner skills. Aims: The current pilot study addressed this lack by training two health practitioners (Diabetes Nurse Educators) in MI, and evaluated the effect of MI training on both practitioner and patient behaviour when MI was delivered in a clinical settting, with patients experiencing difficulties with diabetes self-management. Methods: Comparisons were made between the practitioners’ skills in a baseline condition (Patient Education; PE) and after training in Motivational Enhancement Therapy (MET), a four-session form of MI. At the same time, the effects of the two interventions on patient in-session behaviour were compared. Practitioner and patient data were obtained from transcripts of all PE and MET sessions, which were independently coded using Motivational Interviewing Skills Code therapist and client behaviour counts. Results: Compared with their baseline performance, practitioners, when trained to practice MET, behaved in ways consistent with MI, and this appears to have evoked beneficial in-session behaviour from the patients. Conclusions: These results suggest that the MI training was effective.