Authors experienced a case of mucocele in the left frontal sinus. A 24-year old Korean male soldier was admitted to Capital Army Hospital on May 16, 1980 with chief complaint of dull headache, exophtalmos, visual disturance and intermitant epistaxis on the left side. On physical examination, left turbinates and septum were revealed hyperemic middle turbinate with blood tinged spots and deviated slightly to right side, and we saw round, smooth, rubbery painless swelling within the orbit at the left inner canthus. The left orbital contents were displaced laterally producing proptosis with diplopia. On the radiological examination Caldwell & Waters view showed hazy density in medial side of left orbital and left frontal sinus. Tomography of orbit showed hazy increased mass density with rather sharply defined outer margin left frontal sinus and loss of supermedial margin of left bony orbit probable due to compressive erosion. The case was treated with surgical removal of the Lynch frontal approach, so we present this case with a brief review of the literature.