Paranasal sinus mucocele is a benign expanding lesion and primarily occurs during the third and fourth decades of life. The most common sites are the frontal sinus and frontoethmoid sinus. CT is a best diagnostic tool, while MRI is helpful when there is skull base invasion. The standard treatment is endoscopic marsupialization. We reported a case of an 85-yearold female with left facial pain and smell dysfunction. We arranged a CT scan and the report indicated that the right posterior ethmoid showed a cystic change with intracranial extension. It was arranged for the patient to undergo endoscopic marsupialization. The pathology was a mucocele of the right posterior ethmoid. No complications were noted after the operation.