The treatment of diabetes type 2 is a major challenge for the health care system. According to the International Diabetes Federation (IDF), around 382 million people between the ages of 20 and 79 are currently affected worldwide. The presence of diabetes is associated with personal suffering, impaired quality of life and a deficient treatment leads to complications like retinal ablation, neuropathy, nephropathy and the diabetic-foot syndrome. An appropriate treatment is dedicated to the purpose of adjusting the blood glucose, is very complex and involves many areas of life. Internet-administrated psychological interventions are easily accessible and preliminary evidence suggests that online programs promote lifestyle changes, i.e. nutrition and exercises, of people with diabetes mellitus type 2. However, no trial has yet examined weather a CBT-based internet intervention designed to meet the needs of PwDM can achieve sustained improve adherence behavior like nutrition, physical activity and medication intake, when offered as adjunct to treatment as usual.