The invention relates to a device for projecting patient image data from radioscopic imaging methods and/or tomographic imaging methods onto video images, comprising an image display device (10), at least one video camera (14) and a computer-assisted navigation system which can detect the spatial positions of the image display device (10) and/or the video camera (14) and the spatial positions of a part of a patient's body (1) via tracking means (12, 3) attached to it, wherein the image display device (10) and the video camera (14) are assigned to each other and are realized as a portable unit.