To investigate whether alterations in the cellular component of the trabecular meshwork occur with age, we evaluated trabecular meshwork cellularity and absolute cell number, using specimens obtained from patients ranging in age from newborn to 81 years. We obtained reproducible, quantitative measurements of these parameters, using montages of 1 micrometer meridional sections. A progressive decrease in cellularity (58%) and absolute cell number (47%) in the trabecular meshwork occurred over the 81-year period studied. Regression analysis suggested that the decrease in cellularity and cell number is linear function of age, resulting from a loss of approximately 0.58% of all cells per year. This change in cellularity parallels that seen in the corneal endothelium. implying that trabecular cells, like corneal endothelial cells, may have a limited reparative capacity.