Four consecutive patients with carotid-cavernous sinus fistulas that could not be treated by the standard techniques of endoarterial balloon occlusion or embolization were successfully treated by advancement of a detachable balloon catheter through the ipsilateral superior ophthalmic vein. Under angiographic monitoring, the balloon was passed into the cavernous sinus, inflated to close the fistula, and detached. Three of the patients had a spontaneous fistula, and one had a traumatic fistula that had previously been trapped unsuccessfully. All patients had complete resolution of symptoms and signs after occlusion of the fistula. There were no intraoperative or postoperative complications. The transvenous approach to the cavernous sinus through the superior ophthalmic vein is a safe, effective treatment of carotid-cavernous sinus fistulas, whether they are direct or dural in nature.