We investigated the appropriateness of basing childhood obesity interventions on expectations of return on investment (ROI). We show that excess weight is indeed associated with greater medical expenditures even among children and adolescents. However, under current best practices, it is unlikely that interventions will be able to meet the level of effectiveness required at a low enough implementation cost to show positive ROI. The merits of childhood obesity interventions should be based on their ability to efficiently control weight and improve health compared with alternative uses for available resources. They should not be based on the potential for short-term financial savings.