To clarify whether Reis-Bücklers' and Thiel-Behnke's corneal dystrophies are one entity or whether two distinct corneal dystrophies of Bowman's layer and the superficial stroma (CDB) exist, 28 corneal specimens with clinically suspected diagnosis of CDB were examined by light and electron microscopy, and the literature was reviewed. Eight specimens came from patients with a honeycomb-shaped pattern of opacities at the level of Bowman's layer. Study of those eight specimens disclosed destruction of Bowman's layer, a subepithelial fibrocellular tissue with an undulant configuration, absence of the epithelial basement membrane in many areas and the presence of "curly" collagen fibers with a diameter of 9-15 nm. We concluded that two distinct autosomal dominant CDB exist and propose the designations CDB type I (synonyms: geographic or "true" Reis-Bücklers' dystrophy) and CDB type II (synonyms: honeycomb-shaped or Thiel-Behnke's dystrophy). The eight corneas of our series were characterized as CDB type II. CDB I is clinically characterized by confluent geographic opacities at the level of Bowman's layer, histopathologically by bandshaped granular Masson-positive subepithelial deposits, and ultrastructurally by the presence of "rod-shaped bodies" and may be a superficial variant of granular dystrophy. Visual loss is significantly greater in CDB I, and recurrences after keratoplasty or keratectomy seem to be earlier and more extensive in CDB I. Most cases reported thus far in the literature as "Reis-Bücklers' dystrophy" are CDB II (honeycomb-shaped or Thiel-Behnke's dystrophy).