Corneal buttons from three patients with congenital central corneal leukoma (Peters' anomaly) were examined by light and electron microscopy. All cases exhibited a central absence of Bowman's membrane and iris synechiae to the periphery of the leukoma. In the first patient, extensive keratolenticular adhesion with retrocorneal fibrous tissue filling the central defect of endothelium and Descemet's membrane implicated late anterior displacement of the normally developed lens as the cause of secondary endothelial degeneration. In the second patient, attenuated endothelium and abnormally composed Descemet's membrane indicated primary dysgenesis of the endothelium. In the third patient, the extensive defect of posterior stroma with anterior stromal disorganization and endothelial metaplasia suggested dysgenesis of both the keratocytic and endothelial mesoderm. Thus, although no unified pathogenic mechanism was consistently applicable, either primary or secondary dysgenesis of the corneal mesoderm must be responsible.