In a series of 46 patients accepted for cataract removal and intraocular lens implantation, 23 showed visibly obvious variation in endothelial cell size (polymegethism) according to specular microscopic examination. In this group, mean increase in postoperative corneal thickness was 52.7% on the first postoperative day, 35.4% on the third, and 18.0% after 4 weeks. Mean corneal swelling was consistently and significantly less in the 23 patients exhibiting apparently normal endothelial cell patterns (homomegethism). In homomegethous corneas, preoperative cell density was significantly correlated with age (inversely) and postoperative cell loss (directly). Preoperative cell density in polymegethous corneas showed significant, direct correlation with age, suggesting that endothelial cell density may remain relatively constant in this condition. There was no correlation with postoperative cell loss. Significant differences in endothelial functional capability identified within each morphologically-defined group indicate a structure-function continuum. Since 15 homomegethous corneas and only one polymegethous cornea returned to preoperative thickness within 4 weeks, it appears clinically valid to use morphological criteria in predicting functional capability.