Sixty-five carotid-cavernous fistulas were studied at University Hospital, London, Canada, from 1978 to 1982, 20 of which fulfilled the clinical and angiographic criteria of a spontaneous carotid-cavernous fistula. Of these 20 fistulas, 17 were unilateral, and three were bilateral. In 18 cases the angiographic findings were typical of an arteriovenous malformation (AVM), and in two a ruptured giant intracavernous aneurysm was found. These patients were treated according to whether they had a nonresolving or progressive cavernous sinus syndrome or deterioration of vision. The cavernous dural AVM's were treated with polyvinyl-alcohol and/or isobutyl-2-cyanoacrylate (IBCA) embolization of the external carotid artery blood supply. Two patients underwent postembolization surgical procedures. The detachable balloon technique was used to occlude the fistulas associated with the two giant ruptured intracavernous aneurysms and a small dural intracavernous AVM. Eight patients received no therapy; in two, spontaneous obliteration of the fistula occurred. Of the nine cavernous AVM's embolized with particles and/or IBCA, successful transvascular embolization was achieved in seven cases, and partial embolization followed by surgery in two cases. Successful balloon obliteration of the giant intracavernous ruptured aneurysm was obtained in two cases. In one patient, right hemiplegia with aphasia resulted from reflux of IBCA emboli through the artery of the foramen rotundum into the left middle cerebral artery.