Endonasal surgery is currently extending its application beyond inflammatory sinonasal lesions to successfully treat both benign and malignant neoplasms. This progression has been possible by the detailed information provided by imaging techniques (CT, MRI and PET). Inflammatory diseases are the "domain" of CT. CT provides excellent details about the thin bony sinonasal walls separating the ethmoid from the anterior skull base and the orbit. Benign and malignant neoplasms are the "domain" of MRI because the tumor is more easily separated from adjacent structures, the periosteal linings (periorbita, dura mater) and perineural spread can be accurately shown. Whereas MRI precisely assess pre-treatment tumor extent, early submucosal local recurrences are difficult to demonstrate because of post-treatment changes of the anatomy and of the signal of treated tissues. Though diffusion-weighted imaging and dynamic contrast-enhanced techniques are promising developments, PET-CT may overcome the limits of morphological MRI.