This article provides an overview of the costs associated with overweight and obesity in children and adolescents, and of the cost effectiveness of preventive and therapeutic interventions. First, the results of cost-of-illness studies from the international literature are presented. These studies show ambiguous results, but indicate moderate excess costs due to obesity for this age group. Subsequently, this paper describes the methods that can be used to analyze the cost effectiveness of preventive and therapeutic interventions. Problems arise from the necessity to estimate long-term effects on costs and health consequences of multiple, associated diseases. A number of economic evaluations of preventive and therapeutic interventions published in the scientific literature have reported favorable cost effectiveness. In order to increase the efficiency of health care, more cost-effective services for overweight and obesity should be developed and used.