Medical necessity: do we need it?

The term medical necessity has been mainly a placeholder in insurance plans for over thirty years. More recently, the national health care reform debate and litigation over denials of costly experimental treatments have broken the term out into open discussion about what a necessary service is and who should decide if it is covered. This paper summarizes the history of the term and its evolution from an insurance concept controlled by practicing physicians to a rationing tool used by insurance administrators. How did national reform efforts address this terminology, and how should we define medical necessity in a changing delivery system?