Objectives: This study aimed to provide cost-effectiveness and budget impact analyses of a school-based overweight/obesity screening and care prevention strategy among adolescents. Study design: Cost-effectiveness and budget impact analyses. Methods: Data from 3538 adolescents who participated in a school-based randomised controlled trial in the Northeast of France were used. Costs (from a public payer's perspective) included screening for overweight and obesity and subsequent care. Effectiveness was measured as the change in body mass index (kilogram per square metre), prevalence of overweight/obesity, moderate physical activity energy expenditure, duration and frequency and total sitting time. The incremental cost-effectiveness ratio was calculated, and a budget impact analysis was conducted. Results: The screening and care strategy resulted in an incremental cost-effectiveness ratio of V1634.48 per averted case of overweight/obesity and V255.43 per body mass index unit decrease. The costs for increasing moderate physical activity by 1000 metabolic equivalent of task-min/week, duration by 60 min/week and frequency 1 day/week were V165.28, V39.21 and V93.66 per adolescent, respectively. Decreasing total sitting time by 60 min/week had a cost of V8.49 per adolescent. The cost of imple- menting the strategy nationally was estimated to be V50.1 million with a payback period from 3.6 to 7.3 years. Conclusions: The screening and care strategy could be an efficient way to prevent overweight and obesity among adolescents. Future studies should investigate how the current results could be achieved in schools with different settings and thus justify its relevance for overweight and obesity prevention to policy-makers.