Assessing the costs and benefits of developing a clinical practice guideline is important because investments in guidelines compete with investments in other clinical programs. Despite the considerable number of guidelines in many industrialized countries, little is known about their costs and cost-effectiveness. The authors have developed specific measures to determine the cost-effectiveness of guidelines, using a German evidence-based guideline on obesity for the diagnosis and treatment of obese patients as a model. The measures are: the number of people needed to cure, the number of people needed to prevent from developing the disease in question, and the number of people to treat in order to break even.