Diabetes mellitus as a chronic disease is a major and growing health care problem. Studies on the prevention of severe complications provide evidence for the necessity of tight control. Different interventions and models to achieve strict control and reduce diabetes related risks of complications are available. These are, however, not implemented in daily practice. Our study focuses on this implementation problem: it tests whether implementing professional evidence-based guidelines and best practices -through participation of multidisciplinary teams in the Breakthrough collaborative- results in an improvement of diabetes care, its health outcomes and economic costs.