Corneal endothelial conditions in two children with posterior polymorphous endothelial dystrophy were studied by specular microscopy. The localized vesicular lesions seen by slit lamp formed demarcated blackout areas where two distinct populations of cells were adjacent. Focal areas of highly pleomorphic cells with increased reflective highlights, which may represent epithelial-like cells, were surrounded by enlarged and pleomorphic endothelial cells (background cells). The average background endothelial cell area was three to four times larger than the control area. The composite cells which appeared to coalesce were also observed among the enlarged background cells.