BACKGROUND AND METHODS. To determine the effects of hypertension on brain function, positron emission tomography (PET) studies using (18F)-2-fluoro-2-deoxy-D-glucose (FDG) were performed on a group of 17 otherwise healthy older hypertensive men (mean age +/- SD = 69 +/- 8 yr) and 25 age- and gender-matched controls. Subjects had medically treated essential hypertension for a minimum of 10 years (range = 10 to 24 yr) with no evidence of end-organ impairment from hypertension by routine clinical screening and by history. All hypertensive and control subjects were determined to be cognitively normal by extensive neuropsychological testing. The hypertensive subjects previously had been reported to have lateral ventricle enlargement and left hemisphere brain atrophy by quantitative MRI. PET data were analyzed using t-tests to look at group differences.