The etiology of sinus mucoceles remains somewhat obscure, but favorizing factors can be broadly divided in two: inflammation and trauma. Patients suffering from nasal polyposis offer a unique group for the study of mucoceles as they present the factor of inflammation related to their polyposis, and the factor of trauma when being treated surgically. In order to establish the relationship between nasal polyposis, mucoceles and nasalisation, we performed a retrospective study on the files of 501 patients operated according to the nasalisation technique. We then selected all the patients who also presented with a mucocele that could be diagnosed before, during or after the surgery. We also noted the presence of associated pathologies like bronchial asthma or the Fernand Widal's syndrome (Samter's triad), in order to see if they played a role in mucocele.formation. Our study group finally included 36 patients that presented one or several mucoceles in association with nasal polyposis. Only three of them did not have any antecedent of surgery or known trauma, giving an incidence of mucoceles associated to a non-surgically treated polyposis of 0.6%. The mean incidence rate of mucocele formation after nasalisation for nasal polyposis was estimated to be of 2.5/100 patients per year. The real incidence may be greater as some patients may have been lost in follow up. Sixteen patients presented multiple mucoceles. The most frequent location was the fronto-ethmoidal region. The formation of mucoceles, or their multiplicity, did not appear to be influenced by the presence of an associated pathology, as up to one half of the patients presented an isolated nasal polyposis. Nevertheless, when associated pathologies were present, mucoceles were more frequently observed in the Widal's triad. Most of the mucoceles were diagnosed during the first 6 years after nasalisation, with a peak incidence around year 2 and 3. We conclude that nasalisation, like other endonasal endoscopic techniques, can be related to a greater incidence of mucoceles than non-surgically treated nasal polyposis. Associated pathologies do not seem to influence mucoceleformation. It is important for the surgeon to follow-up patients operated of a nasal polyposis as mucoceles can develop very lately.