Objective. To examine whether training GPs in motivational interviewing (MI) can improve type 2 diabetic patients' (1) understanding of diabetes, (2) beliefs regarding prevention and treatment, and (3) motivation for behaviour change. Methods. A randomized controlled trial including 65 GPs and 265 type 2 diabetic patients. The GPs were randomized in two groups, one with and one without MI training. Both groups received training in target-driven intensive treatment of type 2 diabetic patients. The intervention was a 1 1/2-day residential course in MI with -day follow-up twice during the first year. The patient data stemmed from previously validated questionnaires. Main outcome measures. The Health Care Climates Questionnaire assesses the patient-doctor relationship and type of counselling. The Treatment Self-Regulation Questionnaire assesses the degree to which behaviour tends to be self-determined. The Diabetes Illness Representation Questionnaire assesses beliefs and understanding of type 2 diabetes. The Summary of Diabetes Self Care Activities assesses the extent of various self-care activities related to type 2 diabetes. Results. The response rate to our questionnaires was 87%. Patients in the intervention group were significantly more autonomous and motivated in their inclination to change behaviour after one year compared with the patients from the control group. Patients in the intervention group were also significantly more conscious of the importance of controlling their diabetes, and had a significantly better understanding of the possibility of preventing complications. Conclusion. MI improved type 2 patients' understanding of diabetes, their beliefs regarding treatment aspects, their contemplation on and motivation for behaviour change. Whether our results can be sustained long term and are clinically relevant in terms of changes in risk profile advocates further research.