H~J EALTH CARE plans have enormous potenIItial for contributing to an understanding of the factors influencing the patterns of use of health care facilities and manpower, as well as of the relation between the patterns of delivery of care and the health of a population. Data in the files of health care plans can provide considerable insight into such questions as: What is the relative impact of different forms of organization, such as group practice and solo practice, on the utilization of hospitals? What is the relationship between the method of delivery of health services and the pattern of utilization? What is the quality of care provided in the health care plan? Are some types of plans more acceptable to consumers and providers than others? What impact does the use of allied health manpower have on cost? One of the keys to unlocking this great potential lies in the design of the reporting system for the health care plan. The reporting system must serve several purposes. It must be designed to foster good patient care. It must provide management with the informational tools it needs to maintain an efficient operation and control costs. It should foster research into the factors influencing the use of health care facilities and manpower and into the relationship between the patterns of health care and the health of the population. These several purposes are not mutually exclusive; rather they are complementary. This paper presents the concepts and principles that should guide the development of the reporting system if it is to fulfill these several functions. Instead of approaching the subject in the abstract, the framework to be used is a set of minimal tables prepared by an ad hoc group that grew out of a conference held in the spring of 1970. This conference, supported by the National Center for Health Services Research and Development, Health Services and Mental Health Administration, brought together representatives from six medical schools that were providing, or planning to provide, comprehensive health services (1). To the degree that these schools shared a commonality of purpose, the representatives believed that they should b. able to compile information that would permit a comparison of utilization of services and costs. The Guidelines for Producing Uniform Data for Health Care Plans (2) prepared by the ad hoc working group contain a minimal set of tables. These tables are suggested for use by any health care plan serving a definable population, Dr. Densen is director of the Harvard Center for Community Health and Medical Care, Harvard University School of Public Health, Boston, Mass. The paper on which this article is based was presented by Dr. Densen at the Health Care Evaluation Seminars, McMaster University, Hamilton, Ont.,, Canada, in May 1971. Tearsheet requests to Dr. Paul M. Densen, Harvard Center for Community Health and Medical Care, 643 Huntington Ave., Boston, Mass. 02115.