Case-mix accounting systems have been advanced as both reflecting the economic reality that underlies a hospital's various “product lines”, as defined by DRG prospective payment categories, and facilitating rational decision making regarding resource acquisition, deployment and use. This article uses the institutional perspective to extend this conceptualization of case-mix accounting systems. The institutional perspective proposes that many elements of organizational structure, like case-mix accounting systems, reflect as much a need to conform to societal expectations of acceptable practice as the technical imperative of fostering rationality. This article also extends institutional theory regarding the issues of power and decoupling by considering institutionalization to be an unfinished process in the health-care context, wherein the active agency of individuals and organizations is subjected to systematic examination. In this specific context, case-mix accounting may play a significant role in establishing and perpetuating — not merely supporting — the very social structure of legitimacy, and may consequently be considered an interest-oriented activity having the potential to penetrate and alter the internal operating processes of financially strained hospitals.