Forty-eight cases of posterior polymorphous dystrophy (PPD), diagnosed on the presence of classic vesicles at the level of Descemet's membrane, were studied with the specular microscope. Vesicles alone occurred in 42% and were present in conjunction with PPD bands in 48% and a diffuse abnormality of Descemet's membrane in 10%. It was notable that none of the cases showed ocular abnormalities other than those of the cornea. Endothelial specular photomicroscopy (ESP) revealed distinctive characteristics of PPD vesicles and bands that distinguish them from other posterior corneal abnormalities, e.g., the iridocorneal endothelial syndrome and Haab's striae, which can appear similar at the slit lamp level. The interpretation of the ESP images was that vesicles are pits and bands are trenches in Descemet's membrane only. The endothelium was composed of enlarged cells in almost all cases. Other endothelial abnormalities reported by previous observers were not found. There was evidence that the affected corneas of children were more rigid than normal, and this is discussed in relation to the aetiology of the lesions of PPD.