How do policies regulating medical necessity decision-making influence national health plans? Researchers from Stanford University attempted to answer the following questions: 1) Who are the medical necessity decision makers? 2) How are the terms defined and what information do decision makers use in making their decisions, including what type of evidence and cost effectiveness information is considered? 3) What procedures do health plans use to communicate with physicians and patients throughout the decision making process and to track and use coverage decisions for quality improvement? 4) How can variation in terminology and application of guidelines be reduced? 5) What is the role of accreditation, regulation, legislation, and organizational policies and procedures in promoting clearer definitions and more consistent decision making? and 6) How do the answers to the first five questions vary by the size of the health plan, its tax status, degree of management of care, or geographic region? The objective of this project was to test the findings of a similar project recently completed in California and provide a better understanding of medical necessity decision-making to state and national policymakers.