A major reorganization of a university hospital included the clinical structure as well as the administrative structure of the hospital. The focus of the reorganization was to improve the coordination of patient flows through the hospital. An important part of the organizational change was the introduction of flow managers. The aim of the article is to describe and analyze the challenges of the flow managers in the implementation of the reorganization. The description is based on a number of individual and focus group interviews with professionals and managers on different organizational levels. The analysis is guided by a broad conceptual framework, focusing on the processes of change in a professional organization like a hospital. The results show that the flow managers started with a lot of uncertainty regarding their responsibilities. There was also a lot of resistance to the reorganization, which the flow managers came to personify. They proceeded by building relationships and shaping their role and tasks. They tried to balance proactive and reactive strategies of change. There were some positive results, but they felt that that the expectations placed on them had been unrealistic. The introduction of flow managers in a university hospital has touched upon many elements of the conceptual framework. There were a number of structural, cultural, financial and strategic barriers influencing the change process. The main conclusion of the analysis is that the flow managers need more power and legitimacy in the organization to deal with these barriers. Copyright © 2015 John Wiley & Sons, Ltd.