Patients involved in a clinical trial of cataract surgery who developed psuedophakic bullous keratopathy were studied. They did not differ from the trial population as a whole with respect to their age or pre-operative endothelial cell density. Bullous keratopathy occurred within a narrow range of endothelial cell density.Examination of endothelial cell loss profiles over four years of follow-up after cataract surgery, in patients who developed bullous keratopathy and others, suggested that there was a predictable pattern. A mathematical model is described which gave good agreement between predicted and measured endothelial cell density. The model is now being used to identify parameters which may predict susceptibility to development of bullous keratopathy.