Currently, the estimated number of people with diabetes mellitus is approximately 387 million people worldwide. Due to population growth, urbanization, ageing and the rising prevalence of obesity the numbers of individuals with diabetes is increasing likewise. It has been shown that improving glycemic control is associated with a reduction in late complications of diabetes, such as cardiovascular and microvascular diseases. Therefore, treatment guidelines were established internationally by large and renowned associations and adopted by many countries. For Switzerland only sparse data exist on the actual implementation of such recommendations and on patient's well-being. The Swiss Diabetes Registry - SwissDiab Study is a prospective cohort study aiming at including and collecting data of virtually all patients regularly seen and treated at the study centers (≈ 500 patients each), irrespective of type, duration of diabetes or treatment . This allows the evaluation of diabetes treatment strategies at these centers. Furthermore, risk indicators for micro- and macrovascular complications, mortality as well as costs and quality of life will be assessed. Data will be recorded through an internet-based, electronic database specifically designed for this study. At a later perspective it is planned to extend data collection to general practitioner/family doctor networks in order to include a larger and more representative sample of patients with diabetes in Switzerland.