Clinical preventive services have always been recognized by clinicians as an important part of primary care medicine, but for many years there has been some uncertainty as to the effectiveness of these maneuvers in preventing disease and exactly how and when they should be performed. The recent report of the U.S. Preventive Services Task Force provides a comprehensive review of the science base for preventive services and offers specific recommendations for clinicians on the appropriate delivery of screening tests, counseling interventions, immunizations, and other preventive services. The recommendations provide guidance on how to design an appropriate package of services based on the medical history and risk profile of each patient. This article describes the historical background behind the formation of the task force, its methodology and rationale, and the format of the final report, the "Guide to Clinical Preventive Services." The potential implications of this report and its limitations are also discussed.