A detailed anatomical study of three persistent trigeminal arteries (PTA) is presented. In two cadavers the PTA linked the carotid and basilar systems by traversing the cavernous sinus and lying between the posterior clinoid process and the sensory root of the trigeminal nerve. In the third cadaver the PTA pierced the dorsum sellae and lay in the floor of the pituitary fossa. The potential clinical significance of the course and the possible pattern of blood flow in the vessels is discussed in the light of some recent clinical observations.