Although school-based mental health screening and treatment programs have been proposed as a viable means of reaching youth with unmet mental health needs, no previous reports have attempted to comprehensively document the costs of such programs. The purposes of this report are (1) to estimate the cost of a school-based mental health screening and treatment program in a real-world school setting, and (2) to outline the methods and procedures that should be employed by future investigators to explore the costs of such programs. The program, located in a middle school in a low-income, largely Hispanic neighborhood in New York City, aimed to screen all students in Grades 6-8 for anxiety, depression, and substance use disorders. Most students in need of treatment were referred to the school-based treatment program, where social workers offered individual and group counseling. Economic evaluation methods and a before/after study design were used to assess the costs of the screening and treatment programs for 3 years of operation. Costs were estimated from the societal perspective, which includes all measurable program costs regardless of who bears the costs, and the school perspective, which includes only costs that would be borne directly by a school operating these programs. Data primarily came from administrative records and staff interviews. The total cost ranged from 106,125 dollars to 172,018 dollars for the screening program and from 420,077 dollars to 468,320 dollars for the treatment program. The cost of the screening program ranged from 149 dollars to 234 dollars per student and the cost of the treatment program ranged from 90 dollars to 115 dollars per session. These costs were estimated from the perspective of society. Applying economic cost analysis methods in a real-world school setting is challenging, but the process can generate useful estimates. Cost analyses and cost-effectiveness studies are needed in this area.