he infraoptic course of the anterior cerebral artery (ACA) is a rare vascular anomaly. Early preoperative assessment of this anomaly is important in planning surgical intervention for aneurysms. Purpose. To show the role of CT and MRI for non-invasive diagnostics of the rare concomitant vascular anomaly when planning an intervention for aneurysm rupture.Materials and methods. The article presents a case of a rare combination of unilateral infraoptic course of the A1 segment of the left ACA in a patient with massive subarachnoid hemorrhage from a ruptured aneurysm of the left middle cerebral artery (MCA). The data of neuroimaging methods (CT, CTA and MRI) are presented; the anatomical features of this anomaly and its significance in the planning of surgical treatment and postoperative follow-up are de-scribed.Results. The obtained images (CT, CTA and MRI) demonstrated a massive subarachnoid hemorrhage from the aneurysm of the left MCA and the infraoptic course of the ACA with hypo-plasia of contralateral A1-ACA, which were confirmed intraoperatively.Discussion. The technical capabilities of modern CT and MRI make it possible to study in detail anatomic variations of the cerebral arteries and significantly improve the detection of anomalies and pathological changes in them. Early non-invasive preoperative assessment of the anatomy of the circle of Willis is important in planning surgical intervention, as it increases the safety of dissection of the basal cisterns, isolation and the aneurysm clipping in case of sub-arachnoid hemorrhage (SAH).Conclusions. Identification of anatomic variations of the cerebral arteries and their detailed non-invasive angiographic analysis are important for determining the tactics of open surgery on ruptured aneurysms and planning postoperative follow-up.