Fifty-nine normal dogs, ranging in age from 6 weeks to 132 months were examined with contact specular microscopy to determine the relationship of age to corneal endothelial cell density, morphology, and corneal thickness. Canine corneal endothelial cells appear quite similar to those of other species studied, including man. The hexagonally shaped canine endothelial cells tend to enlarge with age, with the population in young animals averaging around 2500 cells/mm2 and the number of cells in older dogs being frequently below 2100 cells/mm2. A significant increase in corneal thickness was observed with age. Healthy canine corneal endothelial cells appear to maintain a functional monolayer by enlargement and migration and represent a reasonable model for future endothelial cell study.