We describe a patient with a symptomatic left giant carotido-ophthalmic aneurysm who initially underwent coil embolization with subtotal obliteration. The patient's symptoms were initially stable, but 1 year later, she presented with a rapidly progressive contralateral visual deficit. Although angiogram showed a stable neck remnant, MR confirmed aneurysm growth and showed a new peripheral hematoma in the wall of the thrombosed aneurysm. Surgical exploration was undertaken, and even after trapping and intra-aneurysmal thrombectomy, constant bleeding was observed from the wall of the thrombosed aneurysm consistent with the vasa vasorum. Bleeding stopped after cauterization and partial resection of the aneurysm dome, and the aneurysm was clipped. The patient's recent visual deficit markedly improved, and the angiogram did not reveal any residue. Giant aneurysms may continue to grow due to a hypertrophic vasa vasorum and subadventitial hemorrhages. Surgery should be considered if complete thrombosis of the aneurysm does not alleviate patient's symptoms.