Corneal epithelial dysplasia is a rare clinical problem. It is not known whether the corneal epithelial cells undergo dysplastic changes in situ or in the region of the limbal or conjunctival epithelium with subsequent centripetal migration onto the cornea. We obtained an intact, dysplastic corneal epithelial sheet and samples of conjunctival tissue from a 75-year-old patient. Light and transmission electron microscopic examination of the dysplastic corneal epithelium showed histologic evidence of conjunctival, limbal, and corneal epithelium. The adjacent conjunctiva appeared normal except for a possible slight decrease in goblet cells. The 3H-thymidine uptake indicated a normal mitotic index for the conjunctiva. Glycogen content of the dysplastic sheet showed high values seen with corneal and not conjunctival epithelium. The dysplasia recurred despite wide conjunctival resection. Although no final conclusions can be made, we feel our studies support the hypothesis that the dysplastic process in our patient arose de novo in the corneal epithelium.