The aim of the study was to determine the frequency of occurrence and the most common locations of the fenestration of the cerebral arteries, i.e. developmental anomalies consisting of segmental vessel splitting and also the correlation between their presence and the formation of intracranial aneurysms. 6,545 patients in Independent Public Teaching Hospital No. 4 in Lublin in years 2009-2019 who have undergone the angio-CT examination of the head were retrospectively analyzed. The incidence of vascular fenestration was 0.75%, of which 75% were women and 25% men. Reported vascular anomalies most often occurred in the anterior parts of the circle of Willis – ACA (30.61%), AComA (22.45%) and also in BA (30.61%). It has been shown that the occurrence of different types of fenestrations was similar in the group of men and women. There have been diagnosed 11 cases of intracranial aneurysms among patients with observed fenestration (22.45%). For comparison, the incidence of cerebral aneurysms in Western Europe and the US ranges from 2% to 6%. It leads to the conclusion that among patients with fenestration, this type of vascular anomaly occurs much more often, hence they require more frequent control.