The special features of the cerebral hemodynamics were studied in 138 patients with Chiari I malformation (CM) with a help of magnetic resonance angiography (MRA) and transcranial dopplerography (TCD). MRA data analysis (58) revealed the frequent presence of vertebrobasilar system (VBS) maldevelopment and embryonic type of the circle of Willis. TCD data analysis (100) discovered vertebrobasilar insufficiency and bilateral blood flow increase in the intracranial part of the internal carotid arteries giving evidence of the compensated blood flow from the carotid system to the VBS. 21,0% of patients with CM and communicating hydrocephalia had TCD signs of intracranial hypertension. The most significant changes in cerebral hemodynamics were found in patients with marked pathology and elder than 30 years old.