The principal function of the cerebrovascular system is to maintain adequate cerebral blood flow to meet the changing metabolic demands of brain. The brain has only 2% of the body weight, receives 15% of the cardiac output and consumes 20% of the body’s oxygen supply. The vascular system start with four major arteries that provide anterior and posterior cerebral circulation. Physicians must consider anatomical variations of vascular system for understanding of hemodynamics. The cerebral vascular system has three mechanisms for cerebral blood flow: dynamic regulation, autoregulation, and vasomotor reactivity. This article reviews simple flow dynamics, the anatomy of the cerebrovascular system and cerebrovacular system’s ability to control for internal and external conditions. Journal of Neurosonology 2(1):1-4, 2010

Key Words: Cerebrovascular hemodynamics, Anatomy