A cross-sectional study of changes in cat corneal endothelial cell morphology with age was conducted. The central corneal endothelium of 12 kittens and 70 adult cats was photographed using specular microscopy. Endothelial cell density (ECD), coefficient of variation of cell size (used as an index of Dolymegefhism), and cellular shape factor (perimeter2/area) were determined for each animal and analysed as a function of age. We found a rapid non-linear decrease in ECD and polymegethism in the first nine months of post-natal life. Subsequently there was a slight central cell loss of 11 cells/mm2or 0.37% per year during adult life which was not statistically significant. However, polymegethism increased significantly with age during adult life. The shape factor for endothelial cells was 13.61 throughout adult life, indicating that the cat corneal endothelium consists predominantly of six-sided cells. Possible explanations for the finding of no significant decrease in cell density with age could include the higher peripheral ECD in the cat which may compensate for central loss, the short life expectancy of the cat and the large individual variation in corneal diameter.