Morphometric studies of villous epitheliocytes of the choroid plexus of the lateral (glomus) and third and fourth (lateral zone) ventricles of the brain were undertaken in humans aged from 22 to 89 years. Cell height, width, and cross-sectional area were measured, along with the cross-sectional areas of nuclei and cytoplasm for calculation of the nucleus:cytoplasm ratio. These studies showed that epitheliocytes were of variable shape depending on their locations on the surfaces of villi. Epitheliocyte height and the cross-sectional areas of the cytoplasm and cells were greatest in the choroid plexus of the lateral ventricle, while the cross-sectional area of the nucleus and the nucleus:cytoplasm ratio were greatest in the choroid plexus of the fourth ventricle; these features correlate with their functional characteristics. Aging is associated with decreases in the sizes of epitheliocytes and their nuclei and a reduction in the nucleus:cytoplasm ratio, with the development of adaptive rearrangements.