Background: Many school-based recess interventions have been shown to be effective in increasing physical activity but their relative efficiency compared to other school-based programs are unknown. This study examined the cost-effectiveness of Ready for Recess, a program designed to increase students' physical activity in 2 elementary schools. Methods: Standard cost-effectiveness analysis method was used from a program's perspective for this study. Program effectiveness was measured as total metabolic equivalent (MET) hours gained. Program costs included equipment, training, and personnel costs during the 1-year intervention. The cost-effectiveness was measured as the ratio of program costs to total MET-hours gained. Results: Ready for Recess cost $27,643.97 for the 2 schools in the first year of implementation. Physical activity increased by 1.8 MET-hours per day per student. Approximately 32 cents were spent on Ready for Recess to produce an additional MET-hour per student per school day in the 2008-2009 school year. Conclusions: Ready for Recess was cost-effective in its first year of implementation using 35 cents as a benchmark and it was cost-effective relative to other school-based physical activity interventions. The program may be more cost-effective if implemented for a longer time and on a larger scale.