Specular microscopy of the in vivo corneal endothelium of 214 clinically normal eyes in children ranging from 5 to 14 years of age showed a regular mosaic of hexagonal cells. The cell population density of individuals presented some variation, as it doses in older subjects. Quantitative analysis permitted us to determine the normal range of the endothelial cell count at each age. The mean (+/- SD) value ranged from 3591 +/- 399 cells per square millimeter at age 5 years to 2697 +/- 246 cells per square millimeter for the oldest subjects. Our data show a rapid decrease in cell density up to age 10 years. We estimate from our data a decrease in cell density of 13% between ages 5 and 7 years and an additional decrease of 12% by age 10 years.