Mucocele is a benign but expansive cystic formation, lined by a respiratory epithelium. When its content is infected, it is called a mucopyocele. It usually develops in the frontal-ethmoid complex. The maxillary sinus location is exceptional. Case report: a 43-year-old man, presented with chronic unilateral nasal obstruction, purulent rhinorrhea and anosmia. Rhinoscopy showed a bulge in the internal wall of the maxillary sinus emanating from the medium meatus. The computed tomography (CT) showed complete filling of the left maxillary with low-density mass. Magnetic resonance imaging (MRI) confirmed the diagnosis of mucopyocele of the left maxillary sinus. Patient underwent endoscopic surgery with complete recovery. Discussion/conclusion: Mucopyocele of the maxillary sinus is a benign rare lesion, however destructive. A radiological assessment is essential to guide the choice of surgical treatment. The endonasal route remains the reference treatment for this pathology.

Keywords : Maxillary Sinus, Mucopyocele, Mucocele.