Objectives. To investigate cerebrovascular reactivity in patients with diabetes mellitus complicated with cardiovascular autonomic neuropathy. Methods. We examined 34 patients with diabetes mellitus (9 men and 25 women). Functional tests (hypercapnic, cold, orthostatic and others) and indices of cerebral hemodynamics were used for the evaluation of cerebrovascular reactivity. Results. There was a decrease in the rate of cerebral blood flow and the deterioration of cerebrovascular reserves in the middle cerebral artery of patients with diabetes mellitus with cardiovascular autonomic neuropathy and without it in comparison with the appropriate indices of healthy people. At the same time, no differences were found between diabetic patients with - and without cardiovascular autonomic neuropathy. Conclusions. The abnormalities of the cerebrovascular reactivity can play an important role in the pathogenesis of cerebrovascular disease in this group of patients.