Rising levels of childhood obesity present a serious global public health problem amounting to 7 % of GDP in developed countries and affecting 14 % of children. As such, many countries are investing increasingly large quantities of resource towards treatment and prevention. Whilst it is important to demonstrate the clinical effectiveness of any intervention, it is equally as important to demonstrate cost effectiveness as policy makers strive to get the best value for money from increasingly limited public resources. Economic evaluation assists with making these investment decisions and whilst it can offer considerable support in many healthcare contexts, applying it to a childhood obesity context is not straightforward. Childhood obesity is a complex disease with interventions being multi-component in nature. Furthermore, the interventions are implemented in a variety of settings such as schools, the community, and the home, and have costs and benefits that fall outside the health sector. This paper provides a reflection from a UK perspective on the application of the conventional approach to economic evaluation to childhood obesity. It offers suggestions for how evaluations should be designed to fit better within this context, and to meet the needs of local decision makers. An excellent example is the need to report costs using a micro-costing format and for benefit measurement to go beyond a health focus. This is critical as the organisation and commissioning of childhood obesity services is done from a Local Authority setting and this presents further challenges for what is the most appropriate economic evaluation approach to use. Given that adult obesity is now of epidemic proportions, the accurate assessment of childhood obesity interventions to support public health decision making is critical.