Forty-seven mucocoeles of the ethmoid and/or sphenoid sinuses (33 males, 14 females) were operated on during the 10-years period from 1980 through 1989. Thirty-seven cases were post-operative mucocoele, while the remaining 10 were so-called primary mucocoeles. None of the cases had a history of facial trauma. In the majority of post-operative cases, the mucocoele develops 15–24 years after initial surgery. Paranasal sinus surgery in young patients (teenagers) may lead to a mucocoele due to post-operative scarring in the surgical wound. The principal symptoms include globe displacement, double vision, headache, deep orbital pain, a mass in the supero-medial quadrant of the orbit, visual disturbance, etc. Sufficient opening of the mucocoele wall by the endonasal approach is recommended for surgical treatment of ethmoidal and sphenoidal mucocoeles