Minimal invasive endoscopic operations in the paranasal sinuses rely on the detailed knowledge of the individual anatomy, in particular the relationship of the sinus system to neighbouring delicate and vulnerable anatomical structures. Digital CT and MR images are used for 3D reconstruction of the operating field, providing the basis for most 3D navigation systems, guiding the surgeon in close vicinity to delicate structures and so minimising the risk of iatrogenic trauma. We report the application of the ISG Viewing Wand, a computer-assisted navigation system, in endoscopic endonasal surgery related to the anatomy of the paranasal sinuses.