Poor cerebrovascular reactivity is associated with a higher risk of cerebrovascular disease. The most common method to study cerebrovascular reactivity in aging adults, transcranial Doppler ultrasound, yields measurements in large intracranial arteries, but not in regional brain parenchyma that may be more impaired in some disease processes. Measurements derived from transcranial Doppler ultrasound suggest that there are sex differences in cerebrovascular reactivity for aging adults. We investigated the association between age and sex on cerebrovascular reactivity using blood oxygen level dependent (BOLD) magnetic resonance imaging in a representative group of aging adults.