This paper presents an approach to use a semitransparent display as a kind of window into a patient in the context of medical augmented reality (AR) applications. Besides the presentation of the non-off-the-shelf display, the tracking aspects of such an application are the focus of the work presented. In order to allow augmentations of real objects by virtual ones on the display, the user (i.e. physician), the display, the object (i.e. patient) and optional instruments have to be tracked. If required, a tracking system consisting of more than one subsystem, e.g. optical tracking combined with electromagnetic tracking, is used to satisfy all the needs of such a medical application.