The anterior communicating artery (ACoA) is the most frequent site of intracranial aneurysm location. Despite many studies the frequency of aneurysm occurrence with anatomical anomalies is still poorly described. Moreover the significance of the A2 segment of anterior cerebral artery anomalies has been neglected. The aim of this study was to determine the frequency and types of variations of the anterior cerebral circulation in patients with ACoA aneurysms and to analyze their relation to aneurysm occurrence in the Polish population.We studied 50 patients with an established radiological diagnosis of ACoA aneurysm and 100 healthy age- and sex-matched controls using Computed Tomgraphy Angio- graphy. Maximum Intensity and Volume Rendering Projections were used to examine the cerebral arterial circulation. Univariate logistic regression was used to determine the statistical association between ACoA complex anomalies and aneurysm occurrence.Patients in the study group had a significantly higher incidence of hypoplastic A1 seg- ment of the anterior cerebral artery (24% vs. 7%; p0.01) and aplastic A1 segment of the anterior cerebral artery (12% vs. 3%; p = 0.03). The frequency of A1 segment hypoplasia or aplasia in the study group was 36%. There was a statistical trend regarding A2 segment aplasia/hypoplasia as a potential predictor of ACoA aneurysm (6% vs. 1%; p = 0.07).Occurrence of an ACoA aneurysm is associated with hypoplasia or aplasia of the A1 segment of the anterior cerebral artery. A2 segment anomalies may potentially be associated with aneurysm formation.