Bilateral symmetrical absence of the cavernous segments of the internal carotid artery (ICA) and absence of proximal basilar artery with a compensating arterial network (rete mirabile) is quite rare. Although it is found in some lower mammals as a physiological network supplying the circle of Willis, it is associated with ICA hypoplasia or nonpersistence in humans. We present a case of both cavernous ICA and proximal part of basilar artery absence associated with rete formation, which was an incidental finding during cerebral angiography in a 32-year-old woman with a complaint of left maxillary sinus mass.