We experienced a case of huge mucocele involving frontal sinus, and anterior and posterior ethmoid cells ; and exposing large area of anterior cranial fossa, 4×5cm, and superior medial wall of orbita, 2×3cm. A 46-year-old man was admitted to Woo-Suk University hospital on May. 8, 1970 with chief complaints of the severe frontal headache, occular pain, nasal obstruction, protrusion of frontal bone, and exophthalmos for 3 months duration. Inspection and palpation revealed the protrusion of right frontal portion with tenderness, exophthalmos, lacrimination and multiple polyposis. After polypectomy with ethmiodectomy, an exploratory operation (Killian's approach) was performed and we found a huge mucocele of frontal sinus destroying the supero-posterior and inferomedial bony wall of the sinus. Anterior and posterior ethmoidectomy being performed before major operation, we could make a large draining opening through frontal sinus, and anterior and posterior ethmoid cells to the proper nasal cavity. A good result was obtained by the surgical procedure.