In two patients with benign intracranial hypertension, the regional cerebral blood volume was markedly elevated (mean of 85 percent) while regional cerebral blood flow was slightly reduced (mean of 10 percent). Reduction of cerebrospinal fluid pressure by removal of cerebrospinal fluid reduced the mean values of regional cerebral blood volume by 13 percent without significant change in regional cerebral blood flow. The abnormal regional volume and regional flow returned to normal concurrent with the clinical improvement. Venous engorgement and increased intracranial blood volume appear to play an important part in the pathophysiology of increased intracranial pressure in benign intracranial hypertension. A unified concept of the pathogenesis of benign intracranial hypertension is proposed.