Although periventricular hyperintensity (PVH) is frequently detected in elderly persons by magnetic resonance imaging (MRI), the relationship of such lesions with cerebral blood flow (CBF) and cerebrovascular reserve capacity has never been determined. We used acetazolamide-enhanced xenon-133 CBF and MRI to study 28 subjects with one or more cerebrovascular risk factors but with no neurological symptoms. According to MRI examinations on the transaxial slice of the body of the lateral ventricle, 10 subjects had no PVH (group O), 7 a partial PVH (group I), 6 a continuous PVH (group II), and 5 a confluent PVH which spreads over a wide area of the white matter (group III). There was no relationship between the severity of PVH and the resting cortical CBF (F = 2.7). However, the severity of PVH showed significant negative relationships with the acetazolamide-enhanced CBF (F = 9.5; p < 0.01), and the absolute increase of CBF from the resting state to the acetazolamide challenge (F = 5.1; p < 0.01). Our data suggest the importance of hemodynamic factors and the compensatory vasodilation in the pathogenesis of PVH in asymptomatic individuals.