Author was experienced a case of mucocele resolving spontaneously in left frontal sinus. A-23-yesr-old Korean male soldier was admitted to Capital Army Hospital on March 20, 1970, with chief complains of exophthalmos, visual disturbance and intermittent epistaxis on left side. On physical examination, left nasal cavity was revealed hyperemic middle turbinate with blood tinged spots and left orbital contents was displaced laterally producing proptosis with diplopia. The Lynch frontal approach was done. The frontal sinus was revealed thickened mucosa.