As medical technology continues to expand and the cost of using all effective clinical services exceeds available resources, decisions about health care delivery may increasingly rely on assessing the cost-effectiveness of medical services. Cost-effectiveness is particularly relevant for decisions about how to implement preventive services, because these decisions typically represent major investments in the future health of large populations. As such, decisions regarding the implementation of preventive services frequently involve, implicitly if not explicitly, consideration of costs. Cost-effectiveness analysis summarizes the expected benefits, harms, and costs of alternative strategies to improve health and has become an important tool for explicitly incorporating economic considerations into clinical decision making. Acknowledging the usefulness of this tool, the third U.S. Preventive Services Task Force (USPSTF) has initiated a process for systematically reviewing cost-effectiveness analyses as an aid in making recommendations about clinical preventive services. In this paper, we provide an overview and examples of roles for using cost-effectiveness analyses to inform preventive services recommendations, discuss limitations of cost-effectiveness data in shaping evidence-based preventive health care policies, outline the USPSTF approach to using cost-effectiveness analyses, and discuss the methods the USPSTF is developing to assess the quality and results of cost-effectiveness studies. While this paper focuses on clinical preventive services (i.e., screening, counseling, immunizations, and chemoprevention), the framework we have developed should be broadly portable to other health care services.