The human brain utilizes large amounts of O2, which means that the rate of blood flow has to be maintained at a consistently high level. This is made possible by "cerebral autoregulation," the process by which the cerebral and spinal blood vessels keep cerebral blood flow constant, even under change in systemic blood pressure. In addition, cerebral and spinal blood flow and its regulation appear to be closely related not only to vascular disease phenotype but also the pathophysiology of various neurodegenerative disorders, including Alzheimer's disease and amyotrophic lateral sclerosis. In this review, we briefly highlight cerebral and spinal blood flow and its autoregulation and show its relationship to neurological diseases.