An attempt at transfemoral transarterial balloon occlusion of a high-flow spontaneous carotid-cavernous fistula was unsuccessful because the carotid artery rent was too small for this approach. During a subsequent transvenous approach to the cavernous sinus through the jugular vein, the inferior petrosal sinus was perforated. A minor subarachnoid hemorrhage occurred before the tear could be sealed by the deposition of three Gianturco coils in the vein. The patient was taken to the operating room for emergency obliteration of the fistula and petrosal sinus in order to remove the risk of further hemorrhage. Under the guidance of intraoperative digital subtraction angiography, isobutyl-2-cyanoacrylate was injected directly into the surgically exposed cavernous sinus. Successful obliteration of the fistula was achieved with preservation of the carotid artery, and the angiography catheter was removed safely from the petrosal sinus. Although initially after surgery the patient had nearly complete ophthalmoplegia, at her 1-year follow-up examination she had normal ocular motility and visual acuity. The transvenous approach to the cavernous sinus and alternative methods of treatment of carotid-cavernous fistulas are discussed.