To maintain adequate cerebral blood flow despite frequent changes in systemic arterial blood pressure and to constantly adjust blood supply to the current metabolic demand dictated by neuronal electrical activity, brain developed a myriad of mechanisms. These are designed to protect central nervous system from fatal consequences of hypoxia and energy deficit and are collectively called "cerebral autoregulation". Despite years of research mechanisms responsible for regulation of CBF functioning under physiologic and pathologic conditions are still not clear. When these mechanisms are damaged or exhausted, patients life is in danger, as even slight, negligible under normal conditions, systemic hemodynamic disturbances might lead to cerebral infarct. Even perfect imaging of the irreversible brain damage with MR for the particular patient is too late action. Thus, detection of cerebral blood flow disturbances and impaired autoregulation, which are known to be associated with high risk of stroke, are extremely important in clinical practice. Several methods have been developed to quantify this process and thus evaluate risk of cerebral ischemia and guide therapeutic process. This review focuses on current knowledge on physiology of regulation of cerebral blood flow, mechanisms responsible for brain damage resulted from cerebral ischemia and reviews noninvasive diagnostic tests to assess cerebral autoregulation.