The 1965 legislation that established Medicare and Medicaid declared that the Federal Government would not interfere in clinical medicine. Despite the original intent, Medicare and Medicaid have had tremendous influence on medical practice. In this article, we focus on four policy areas that illustrate the influence of CMS (and its predecessor agencies) on medical practice. We discuss the implications of the relationship between CMS and clinical medicine and how this relationship has changed over time. We conclude with thoughts about potential future efforts at CMS.