Histologic and micrometric studies have been performed to examine changes with age in the kidney of 100 autopsy cases ranging from 1 to 70 years of age. The number of tubular cells and glomerular cells decreased significantly during aging. The number of glomerular tufts per unit area also decreased significantly with advancing age. The size of malpighian corpuscles, glomerular tufts, nuclei of glomerular cells and nuclei of tubular cells increased significantly in senile kidneys. The statistical analysis revealed that the values of the coefficient of variation generally increased with advancing age.