RÉSUMÉ
Introduction: Despite being quite common, there is little information concerning the Brazilian population on anatomic variations and anomalies in the brain circulation. This study intends to describe the most common variations found during the autopsies for the AMA Study. Material and methods: Fifty cadavers had their circle of Willis dissected and analyzed. Results: 54% presented at least one variation, and they were more common in the posterior circulation (88.5%) and on the right side of the brain (59.7%); non-classical morphology was more common bilaterally and in the posterior circulation of the circle of Willis (37.1%). The most common finding was the absence of the posterior communicating artery (32%), followed by posterior cerebral arteries originated from the internal carotid artery (18%). There were no variations in the middle cerebral arteries. Accessory anterior cerebral arteries were present in 6%, and A1 segment hypoplasia was present in only 2% of the cases. Conclusion: Brazilian population variations are in accordance with the literature and there seems to be no difference between races in the variation of brain circulation.