The absence of the internal carotid artery (ICA) is a rare congenital anomaly. Diagnosis of this entity is important because of its association with the cerebral aneurysm and also indicated during planned carotid or transsphenoidal surgery in thromboembolic disease and in the surveillance and detection of associated cerebral aneurysms. We report a case of congenital absence of unilateral ICA with associated cerebral aneurysm of the anterior cerebral artery.