These last years the surgical treatment of inflammatory ethmoid disease has been completely modified, with new endoscopic conservative procedures. In a preoperative phase it is mandatory to provide optimal CT imaging of the ethmoid labyrinth, and for this purpose sections perpendicular and parallel to the nasofrontal duct axis are better than axial and coronal slices. The anatomy of the ethmoid is fairly complex; however certain constant anatomic landmarks allow a systematic analysis of the ethmoid labyrinth: the unciform process, the bulla, the middle turbinate, the superior turbinate and their respective basal lamellae.