In dyskeratosis congenita, the hyperkeratotic lesions affecting the mucous membranes have a propensity to undergo malignant change. Unfortunately there is presently no reliable method for predicting such an outcome. Oral mucosal biopsies were obtained from a case of dyskeratosis congenita and keratin expression identified using a panel of antikeratin antibodies. Marked changes were found from keratin profiles established for normal oral mucosa. In particular coexpression of three separate type 1 keratins (K16, K10 and K13) were observed in the ventral tongue lesion. The keratin pattern found in the tissue biopsies examined is suggestive of an unusually immature or disturbed state of tissue differentiation, and as such may be indicative of future malignant change.