Hyperperfusion syndromes comprise a group of disorders in which excess cerebral blood flow plays an important pathophysiological role. The major disorders considered here are hypertensive encephalopathy, eclampsia, and posthyperperfusion syndrome as seen in patients after carotid endarterectomy. We have an incomplete understanding of all of these disorders, and controversy exists about the degree to which factors other than hypertension and hyperperfusion contribute to the syndromes. This chapter reviews the pathophysiology of these disorders, addressing our basic knowledge of cerebral hemodynamics as well as some of the persisting controversies. The chapter then addresses epidemiology, clinical presentation, diagnosis, and management.