A case of a patient with a giant aneurysm of the left middle cerebral artery and a huge arteriovenous malformation hemodinamically related is reported. Complete thrombosis of the aneurysm was observed after extirpation of the arteriovenous malformation as shown by angiography one week, six months and a year post-operatively. Reduction of the regional cebral blood flow after extirpation of the arteriovenous malformation and the natural tendency of these giant aneurysms to partially thrombose were to be the explanation for our result.