The invention relates to an image guided surgery system comprising —a surgical instrument (14), —a tracking system for locating and tracking an object (20) in a surgical environment, the tracking system including a tracking sensor system, in particular a tracking camera system (16); and —a medical navigation system (15) processing tracking data from the tracking system and image data of the object (20), and outputting image data and navigational assistance on a display (13). The instrument (14), the tracking system including the sensor system (16) and the medical navigation system including the display are integrated in one single portable unit (10), or the instrument (14) and the medical navigation system including the display are integrated in one single portable unit (10), while at least the sensor system (34) of the tracking system is arranged at a location near a region of interest determined by the object (20) and the field of surgery.