This article addresses the issues of scaling health information system in the context of developing countries by taking a case study from Ethiopia. Concepts of information infrastructure have been used as an analytical lens to better understand scaling of Health Information systems. More specifically, we question the fruitfulness of focusing on not being installed base hostile and suggest focusing on how to be installed base “friendly” by underscoring how the installed base can also be draw upon and shaped by human agents. The paper conceptualizes health information infrastructure (HII) building as an intertwined process of the evolution of the installed base and the construction activities of human agents. Overall, we argue that it is not only the adverse situation that determines how things develop, but HII builders need to navigate and take into account a wide range of issues related to the installed base. The relative strength between the proponents of a HIS and the installed base will vary and thus require different approaches. While the II may develop and evolve as it is out of control from time to time, this study shows that there is also room for II building activities at certain points in time.