Clinoidal meningiomas. Anterior clinoidal meningiomas are frequently grouped with suprasellar or sphenoid ridge meningiomas, masking their notorious association with a high mortality and morbidity rate, failure of total removal, and recurrence. To avoid injury to encased cerebral vessels, most surgeons are content with subtotal removal. Without total removal, however, recurrence is expected. Recent advances in cranial-base exposure and cavernous sinus surgery have facilitated radical total removal. The author reports 24 cases operated on with vigorous attempts at total removal of the tumor with involved dura and bone. This experience has distinguished three groups (I, II, and III) which influence surgical difficulties, the success of total removal, and outcome. These subgroups relate to the presence of interfacing arachnoid membranes between the tumor and cerebral vessels. The presence or absence of arachnoid membranes depends on the origin of the tumor and its relation to the naked segment of carotid artery lying outside the carotid cistern. Total removal was impossible in the three patients in Group I, with postoperative death occurring in one patient and hemiplegia in another. Total removal was achieved in 18 of the 19 patients in Group II, with one death from pulmonary embolism. In the two patients in Group III, total removal without complications was easily achieved. 