This study outlines the vascular territories of the cerebral arteries that originate from the Willis circle to supply limbic structures in the guinea pig brain. The entire cerebral vascular system was visualized in four preliminary experiments by performing superselective microangiographic studies with iodine contrast medium perfusion of the whole brain after in vitro isolation according to a technique described previously (de Curtis et al. [1991] Hippocampus 1:341-354). Subsequently, the perfusion territory of the different arteries that originate from the Willis circle was characterized after cannulation and perfusion of individual arteries with a gelatin solution that contained waterproof black ink. The analysis was performed by identifying the brain regions that contained the black stain on 150-ยตm-thick coronal sections that were cut after brain fixation with paraformaldehyde for at least 1 week. The middle cerebral artery and the rostral and caudal posterior cerebral arteries supply the limbic cortices and some related subcortical regions. In particular, large portions of the hippocampal formation are supplied by both the rostral posterior cerebral artery and the rostral branch of the caudal posterior cerebral artery, whereas the ventral temporal part of the hippocampus is served exclusively by the rostral posterior cerebral artery. The amygdala, the periamygdaloid cortex, and the piriform cortex are served by the middle cerebral artery and in part by the perforating arteries. The entorhinal, perirhinal, and postrhinal cortices are vascularized by the posterior and middle cerebral arteries, with a very broad overlap between the distal territories of these vessels. The demonstration of an extensive superimposition between the arterial supply of the entorhinal and the perirhinal regions suggests the presence of anastomotic connections that potentially are protective against ischemic events. Such an arrangement was not observed for the arteries that supply the ventral portion of the hippocampal formation and the basolateral amygdala, which showed nonoverlapping boundaries. The pathophysiological consequences of a similar vascular organization are discussed.