During examination of 131 penetrating keratoplasty specimens from patients with keratoconus obtained in an 11-year period, we observed two histopathologic variants based on the appearance of Bowman's layer and the corneal epithelium. "Typical" keratoconus specimens had multiple breaks in Bowman's layer and central epithelial thinning, whereas "atypical" corneas lacked breaks in Bowman's layer and had less thinning of the central epithelium. Ninety-five corneas were from patients who underwent grafting in only one eye. Seventy-six (80%) of these corneas were "typical" and 19 corneas (20%) were "atypical" in appearance. Both variants had similar degrees of central stromal thinning. Patients with "typical" and "atypical" corneas differed demographically by race only; 49% of "typical" and 95% of "atypical" corneas were from white individuals. Thirty-six corneas were from 18 patients who underwent bilateral penetrating keratoplasty. The histologic appearance of these corneal pairs was concordant in 13 patients and discordant (one "typical" and one "atypical" cornea) in five patients. Statistical analysis indicated that this distribution is not significantly different from that predicted by chance and suggests that "typical" and "atypical" corneas are manifestations of the same disease process.