Twelve patients with nasal polyposis were examined with magnetic resonance imaging (MRI) prior to surgical ethmoidectomies (20 ethmoidectomies). MRI signal was analyzed in correlation with surgical findings in order to define the semiology of nasal and sinuses polyps. One of the most important point of this semiology is based on the analysis of sequences after administration of gadolinium. MRI seems an interesting method for analysing the extension of nasal polyposis and could be useful for ENT surgeons before an endoscopic nasal surgery.