In this paper we investigate the IT systems silo problem in e-health infrastructures. After three decades of user oriented systems development the health sector is characterized by system diversity and fragmentation. In response to this situation health authorities in the EU countries have called for a strategy of standardisation and integration; aiming to reduce complexity. It is assumed that this strategy will lead to less costly (through better co-ordination) and better health services (through more reliable data). Our research question is, how can we understand and manage the socio-technical complexity of large-scale integration in e-health? \ \ Our empirical evidence is a large e-health programme taken by the Southeast Regional Health Authorities in Norway, in order to reduce the number of systems and user environments. In particular we investigated the implementation and integration of an electronic patient journal system for 12.000 users. Considering our findings, and building on infrastructure and complexity theory, we find that the current approaches to resolve silo integration are relatively effective in reducing organisational complexity, but they may increase overall complexity over time. \