Effects of a cognitive behavioural treatment (CBT) in type 2 diabetes patients were studied in a randomised controlled trial. Patients were recruited from a diabetes care system (DCS). The intervention group (n = 76) received managed care from the DCS and CBT. The control group (n = 78) received managed care only. Effects on risk of developing coronary heart disease (CHD), clinical characteristics, lifestyle, determinants of behaviour change, quality of life, and depression were assessed after 6 and 12 months. The intervention did not result in a significant reduction of CHD risk (difference between intervention and control group was -0.32 % (95 % CI: -2.27; 1.63). The amount of heavy physical activity increased significantly in the intervention group at 6 months [intervention versus control group was 20.14 min/day (95 % CI: 4.6; 35.70)]. Quality of life and level of depression improved as well. All effects disappeared after 6 months. No effects were found on clinical characteristics.