Aim:Anatomical variants of the circle of Willis are diverse and frequent and, although they are not a direct cause of cerebrovascular diseases, they are risk factors for impaired collateral perfusion and wall shear stress. This study aimed to correlate the anatomical variants with their effects on the hemodynamic and geometrical parameters responsible for the pathogenesis of neurological diseases.Material and Methods:The circle of Willis and the proximal segments of the main arteries were dissected and measured on ten formalin-fixed human brains. The anatomical variants were systematized using descriptive statistics. The mathematical models for brain perfusion and wall shear stress were developed by optimally approximating resistance to flow, vascular conductance, and branching.Results:80% of the brains presented asymmetries, especially in the posterior communicating (70%) and anterior cerebral (40%) arteries. The posterior circulation had more variations (65.21%). Nine hypoplastic vessels were found in 7 brains. Atypical origins were observed in eight cases. According to the mathematical models, which integrated each anatomical change in the global circle of Willis anatomy, the circle of Willis’ geometry could represent a risk factor for intracranial aneurysms and atherosclerosis, mostly when hypoplastic arteries are present, due to high resistance to flow and imbalanced bifurcation geometry. Accessory vessels are less associated with cerebrovascular risk.Conclusion:We described anatomical variants of both the anterior and posterior circulations and their specific effects on the hemodynamic balance of cerebral blood flow.