Trephination of the frontal sinus is the one of the effective external approach to the frontal sinus problems and is useful for both diagnostic and therapeutic purposes. Indications for trephine operation include (1) acute or subacute suppurative frontal sinusitis, (2) pott's puffy tumor, (3) fracture of the frontal sinus, and (4) exploratory procedures for biopsy and determination of the nature of chronic frontal sinus disease. Its diagnostic and therapeutic goals are to establish the drainage, to prevent the intracranial complications, to inspect the sinus status and to insert the instruments for the reduction of the fracture. We report cases of frontal sinus trephination in patients with acute frontal sinusitis (3 cases), frontal sinus fractures (2 cases) and malignancy of the frontal sinus (1 case) with review of the literatures.