The aim of the present study was to determine the prevalence of long-term mucocele development after functional endoscopic sinus surgery (FESS) for nasal polyposis, to search for a statistical relationship with preoperative variables and to analyze the management of this complication. A retrospective analysis of 153 patients who underwent FESS for nasal polyposis, with a minimum of 7 years of follow-up, was performed. Mucocele diagnosis was based on regular clinical and radiologic evaluation. Univariate and multivariate statistical analysis was performed. The postoperative mucocele rate was 13.1% (20 patients). The mean delay between surgery and mucocele diagnosis was 6.25 years. A high preoperative Lund-Mackay score (>19) was a risk factor for postoperative mucocele (p = 0.04). Asthma and aspirin intolerance did not increase the risk of this complication. Endoscopic marsupialization of mucoceles was successful in 19 patients, with only one recurrent frontal mucocele. One patient required external approaches for two frontal mucoceles. In conclusion, mucocele risk after FESS for nasal polyposis is significant, especially in case of a high preoperative Lund-Mackay score (>19). Long-term clinical follow-up is recommended, imaging being prescribed based on symptoms or abnormal findings on clinical examination. Endoscopic marsupialization is very effective, but frontal mucoceles are more likely to recur.