To assess the influence of donor age, donor endothelial cell density, recipient age, and diagnosis on loss of endothelial cell density after penetrating keratoplasty, we evaluated endothelial cell density data from specular endothelial images collected during the follow-up penetrating keratoplasty surgeries performed from 1980 through 1985 at one center. Univariate and multivariate analyses of information from 265 grafts showed consistent and statistically significant associations between 1-year postoperative loss of endothelial cell density and donor age, donor endothelial cell density, and recipient age. Corneas obtained from older donors, corneas with higher donor endothelial cell density, and corneas transplanted to older recipients demonstrated greater percentage of loss of endothelial cell density 1 year after surgery. These three factors accounted for 17% of the total variance in percentage of loss of endothelial cell density 1 year after surgery.