Cerebral blood flow was studied in nine patients with idiopathic pseudotumour and one patient with cortical vein thrombosis in Denver, Colorado using the 133Xe inhalation method. Globally elevated blood flows were found in all of the idiopathic pseudotumour patients averaging 149% of control values generated in the same setting. The patient with the cortical vein thrombosis demonstrated normal global flows. Possible pathophysiological mechanisms for these findings are discussed.