Two patients are described, the first with a giant aneurysm of the left carotid bifurcation previously treated by endovascular technique, the second with a bilateral intracavernous aneurysm: both were submitted to high-flow by-pass operation. The first patient was a 40 year-old woman who had presented subarachnoid hemorrhage 6 months before operation. She had been treated by means of a high-flow by-pass between the external carotid artery and the middle cerebral artery. Control angiograms performed 12 hours later showed a stenosis above the suture between the external carotid artery and the venous graft. Angioplasty was performed by endovascular route: new angiograms showed occlusion of the graft while dopplersonography demonstrated the presence of flow within the graft. Angiograms performed 1 week later showed marked vasospasm of the venous graft, of the internal carotid artery, the anterior cerebral artery and the middle cerebral artery. The evolution of spasm of the graft and of the intracranial arterial flow was monitored by dopplersonography and MR-angiography: the latter was performed 20 days after the last angiography and confirmed patency of the graft, while dopplersonography showed resolution of vasospasm. Finally, the aneurysm was embolized. The second patient was a 49 year-old woman with mild left palpebral ptosis and retro-orbital pain. She had already been submitted to high-flow by-pass operation 7 months earlier to treat a right intracavernous aneurysm; the left by-pass was necessary because the intracavernous aneurysm had become symptomatic. One week after surgery, spasm of the venous graft was documented by MR-angiography. In both cases, treatment consisted of calcium antagonists as well as hypertensive and hypervolemic medication, which was successful in treating vasospasm of the venous graft and its symptoms. Spasm of the venous graft, a well-known occurrence in cardiac revascularization, can also be observed in cerebral revascularization.