Atrophy of brain matter in hypertensive and normotensive subjects was studied by quantitative measurements of brain volume and cranial cavity volume using x-ray computed tomography. The 123 normotensive subjects ranged in age from 20 to 79 years and were divided into six ten-year age groups. The 67 hypertensive subjects ranged in age from 40 to 83 years and were divided into four age groups. Values of the brain volume index ( BVI ), the ratio of brain matter volume to cranial cavity volume, for hypertensives and normotensives in the same age groups were compared. Mean BVI values were significantly lower in hypertensives in the fifth (P less than 0.01), sixth (P less than 0.01), seventh (P less than 0.05) and eighth and ninth decades of life (P less than 0.001). Systemic hypertension, which may induce various diseases in the elderly, had a striking effect on atrophic changes of brain matter in elderly subjects.