Advanced visualization is getting increasingly important for the operation room of the future. The increasing number of available medical images must be presented to surgery team in new ways in order to support them rather than overloading with more information. In our project NARVIS we integrate an HMD-based (head mounted display) AR system into the operation room for 3D in situ visualization of computed tomography (CT) images. The final system aims at spinal surgery. The work is in close collaboration with our project partners “Klinikum für Unfallchirgie” at LMU, A.R.T. Weilheim, and Siemens Corporate Research in Princeton. The project is funded by Bayerische Forschungsstiftung.