A case of frontal sinus mucocele is reported. A 72-year-old man, complained of swelling of the upper eyelid. Examination revealed the presence of a cyst in the frontal sinus. The frontal sinus was opened by Killian's method and the frontal sinus mucocele was removed. The wall of frontal sinus was partially destroyed and the dural surface was widely exposed. Two days after the operation, computed tomography showed evidence of space occupying lesions severely pressing the frontal lobe. However,

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... e patient did not complain of psychiatric symptoms and there was no presence of suspected meningitis. This means that the mucocele grew very slowly. The patient completely recovered and there has been no trouble after the operation.