This report documents the treatment of a giant aneurysm of the internal carotid artery bifurcation with a fistula to the cavernous sinus, which appeared following closed head trauma. A 39-year-old man suffered from a blunt head trauma in an automobile accident. Two weeks after the trauma, progressive chemosis of left eye was presented. Four months after the trauma, digital subtraction angiography showed an internal carotid artery bifurcation aneurysm, with drainage into the cavernous sinus. The lesion was successfully obliterated with preservation of the parent artery by using coils in conjunction with Onyx. Follow-up angiography obtained 3 months postoperatively revealed persistent obliteration of the aneurysm and fistula as well as patency of the parent artery. Endovascular treatment involving the use of coils combined with Onyx appears to be a feasible and effective option for treatment of this hard-to-treat lesion.