The author has recently experienced two cases of the otogenic subdural abscess accompanied by chronic suppurative otitis media. Case I was treated by radical mastoidectomy and trepanation with extensive subtemporal craniectomy after preoperative right carotid cerebral angiography. Radical mastoidectomy with incision and evacuation of the pus in the sigmoid sinus was performed in the case 2. Secondary drainage of the subdural abscess through the inner wall of the sigmoid sinus was done. The author was strongly impressed that the carotid cerebral angiography was very helpful in diagnosis of the diffuse subdural abscess like case 1.