In the first part of this investigation, 216 consecutive carotid angiograms from 108 patients were reviewed to analyze variations of the anterior choroidal artery (AChA) for the origin, size, and course of the stem and for the possible identification of the uncal branch, perforating branches, and plexal segment of the AChA. In the second part of our investigation, we analyzed anomalies of the AChA seen on angiography. The anomalies of this artery were divided into hypoplastic and hyperplastic types, with prevalences of 3% and 2.3%, respectively, as determined from 216 control carotid angiograms. Hypoplasia of the plexal segment of this artery might represent an evolutionary variant in which the artery ceased to acquire choroidal branches, thus remaining in the reptilian stage. Twenty-five hyperplastic anomalous arteries that supplied a part of the distribution of the posterior cerebral artery were found not only on the 216 control angiograms (five arteries), but also on 2000 carotid angiograms obtained over 8 years (20 arteries). The hyperplastic arteries were further classified into subtypes according to the distribution area and course of the vessel. The hyperplastic anomalies are considered to represent a situation in which the AChA has maintained, as a main pathway, an anastomosis with the posterior communicating artery and posterior cerebral artery. Our detailed analysis of the variations and anomalies of the choroidal artery should be useful in the assessment of this territory.