The costs and effectiveness of asthma action plans for children were evaluated in a cross-sectional economic analysis. Direct health care and indirect costs, nights with symptoms, and asthma attacks were measured in 879 Ontario children with asthma. From a societal perspective, the total annual costs of the asthma action plan and the control groups were CDN$6,948 and CDN$6,140 per patient, respectively. Health outcomes were similar. The difference in cost was attributable to greater medication and health services use in the intervention group. Prospective randomized trials are necessary to measure potential improvements in control of asthma using asthma action plans.