Aim: An assessment of increased compensatory blood flow in the brain-supplying arteries in patients with significant carotid artery stenosis. Materials and methods: Doppler ultrasound was performed in 218 patients over 60 years of age to evaluate both the degree of brain-supplying artery stenosis as well as the blood flow volume balance in all vessels supplying the brain: the internal carotid artery, the external carotid artery and the vertebral artery. The control group included 94 patients with no stenosis in the extracranial segments and no neurological manifestations, in whom blood flow values were calculated (the internal carotid artery – 290 mL/min, the external carotid artery – 125 mL/min, the vertebral artery – 80 mL/min); the total mean blood flow in the brain-supplying arteries was 985 mL/min. A 33% increase in blood flow was considered compensatory. In addition to the control group, 30 patients with asymptomatic stenosis of less than 50% and 12 patients after endarterectomy with mean blood flow of 920 mL/min and 960 mL/min, as well as two groups of particular interest to us, i.e. 38 patients with no compensatory blood flow increase despite significant stenosis (>50%) with mean blood flow of 844 mL/ min and 44 patients with similar stenosis and with compensatory blood flow increase up to 1174 mL/min were included in the analysis. Results: Comparison of the two groups showed several significant differences: increased blood flow (118% vs. 86% of the norm) in patients with compensated stenosis, an increased number of asymptomatic patients (70% vs. 37%) and a threefold increase in the number of patients with occlusions (15 : 5) in the group of patients with increased blood supply to the brain. Conclusions: All potential blood-supplying vessels, including the external carotid artery, are involved in brain tissue perfusion in some of the patients with significant stenosis. Determining the degree of compensation may have an important impact on the indications for surgical treatment, which will make a valuable contribution to the current criteria (asymptomatic/ symptomatic patients).