• Two unrelated boys had a history of bilateral corneal clouding at birth following uncomplicated full-term gestations and spontaneous vaginal deliveries (without forceps). Clinical examinations disclosed bilateral corneal edema, no inflammation, and normal intraocular pressures. There was no history of similarly affected family members. The patients underwent penetrating keratoplasty at ages 4 months (patient 1) and 12 years (patient 2). Light and electron microscopic studies of the corneal buttons from both patients revealed areas of degeneration of the endothelium and separation of rounded endothelial cells. The morphologic features were strikingly similar to those in two acquired forms of corneal disorders—autoimmune endotheliopathy and "acute endotheliitis." Immunocytologic and in situ hybridization studies for herpes simplex virus were not consistent with either productive or latent corneal infection. Ultrastructural changes in Descemet's membrane reflect delayed or abnormal development of the postnatal nonbanded layer in patients 1 and 2, respectively. These suggest an intrauterine insult that resulted in endothelial dysfunction. The histologic and ultrastructural features of these two congenital cases are not typical of those seen in any of the recognized causes of congenital corneal clouding. We propose that these cases represent a unique congenital corneal endotheliopathy of undetermined origin.