This paper analyses how diagnoses comprise a central component in the governance infrastructure of health care. A view upon diagnoses as ‘governance hybrids’ enables a perspective that sees diagnoses simultaneously as designating patients’ diseases and their accountable value in the system of Diagnosis Related Groups (DRG). DRG is an internationally widespread system that categorises patients into groups that are clinically meaningful and have approximately the same average costs. Based on Science-Technology-Society studies (STS), the paper analyses how diagnoses transgress their clinical functions and are transformed into DRG in a governance infrastructure that connects the state, regions and hospital departments. The aim is to contribute to an understanding of diagnoses as
infrastructuring and hence as both parts of an infrastructure and as performative elements with societal consequences. The paper presents analyses of (i) how diagnoses play a central role in a historical change in the power relations between clinicians and the state, (ii) how processing of diagnoses through DRG becomes an administrative matter requiring new special competences and functions, (iii) how diagnoses as part of DRG enables financial modeling and pursuance of governance goals that were not previously possible, and finally (iv) how the DRG system has spurred criticism due to its perceived effects as an incentive system. Lastly, the paper reflects upon how the DRG system can be regarded as an infrastructure that develops and constitutes society, because it gathers and creates mutually involving interactions between political, administrative and healthcare professional domains. Thus infrastructures such as DRG are not only tools, but also societal actors.