Posterior polymorphous endothelial dystrophy and iridocorneal endothelial syndrome share common specular microscopic findings, clinical course, and some histopathological features. Despite differences in inherited trait and severity of disease a common pathogenetic mechanism for the two diseases is suggested. This consists of congenital epithelialisation of the posterior corneal surface during embryogenesis with migration of these cells around the anterior segment uninhibited by surrounding normal endothelium.