Cerebral aneurysms coexistent with iatrogenic (after surgical ligation or occlusion) or idiopathic (due to atheromatosis) occlusion of an extracranial cerebral artery are very rare. The occlusion of the brachiocephalic vessels leads to the formation of a collateral circulation at two levels: the circle of Willis and the connections between collaterals of the extracranial cerebral arteries. The authors discuss different types of collateral arterial pathways as well as hemodynamic abnormalities in the case of the occlusion of the brachiocephalic vessels, particularly internal carotid artery or the innominate artery occlusion. The paper analyses the etiopathogenesis of cerebral aneurysms in view of the hemodynamic theory of cerebral aneurysms formation. The article is illustrated with own three cases of ruptured cerebral aneurysms coexistent with the occlusion of the innominate artery.