Fusiform aneurysms are unusual, and they are most found in the vertebrobasilar system. Although the presence of such aneurysms has been related to atheromatous degeneration of the arterial wall, in many cases the cause of their formation is unknown. The clinical manifestations of fusiform aneurysms of the vertebrobasilar system are generally due to mass effect with compression of adjacent structures or to ischemic events; exceptionally they are due to subarachnoidal haemorrhage. We present the case of a patient with symptoms suggestive of brainstem ischemic damage, in which neuroimaging showed a fusiform aneurysm of the basilar artery with an intraaneurysmatic thrombus. Antiaggregation did not prevent new ischemic events, so anticoagulation therapy was initiated. The patient remained asymptomatic at 8 months of follow-up. The treatment of fusiform aneurysms is controversial; however, there are some evidences in the literature supporting that patients with ischemic events may be treated with long term anticoagulation, especially in cases of non-giant aneurysms of the vertebrobasilar system not accompanied by aneurysms in other sites.