Background: The comparison the variants of the cerebrum arterial circle in people who have not suffered from the disorders of the cerebral circulation and in people with this pathology help to determine the risk of cerebrovascular diseases, it being the aim of the research. Material and methods: The variants of the cerebrum arterial circle in 425 adults (aged 17-90) who had died of causes not related to the cerebral circulation disorders and had not suffered from hypertension, connective tissue diseases and diabetes were examined macro- and microscopically. The structure variants of the circle of Willis in 100 people (aged 1785), suffering from cerebrovascular diseases were studied by means of computerized tomography (in vivo study). Results: The variants of the cerebrum arterial circle in people with no disorders of cerebral circulation were established. Classical variant of the structure was found in 34.35% of cases; non-classical variants account for: “rare variants” (25.41%), posterior trifurcation of the internal carotid artery (15.76%), aplasia of the posterior communicating artery (14.36%), combined variant of the circle structure (10.12%). In people with cerebrovascular diseases the circle of Willis is represented only by non-classical variants which are revealed in 8-21% of cases more frequently than in people without this pathology. Conclusions: Such non-classical variants of the circle of Willis as the combined variant, the absence of one (or both) posterior communicating arteries, posterior trifurcation of one internal carotid artery contribute to the development of cerebral circulation disorders, and therefore people with the above mentioned variants form the risk group.