Recently the construction industry has started to study and implement together Lean Construction (Lean) and Building Information Modeling (BIM) to better manage projects. Previous research findings suggest that several changes in the work practice and business processes are needed to fully take advantage of BIM and Lean. Even if the client's role is very important to drive the entire process, the literature lacks of comprehensive examples of client's implementation. The paper shows how a large client organization is integrating Lean and BIM in real projects and how it is possible to measure it thanks to a Maturity Matrix. The research is based on a case study involving both active participation and interviews. The main results indicate that a) internal change is needed in the client organization; b) clients need to drive the process in order to maximise benefits; c) BIM does not fit in the traditional procurement process; and d) existing contracts need to be modified to support BIM and Lean. Research findings are useful for large client organizations that would like to integrate BIM and Lean in their operational strategy as well as for researchers. Further studies could be done to compare the work of different client organizations.