We report on a 32-year-old female patient with chronic diabetes mellitus, type I, and chronic renal failure, who developed the typical clinical picture of hyperkeratosis follicularis et parafollicularis in cuteum penetrans (Kyrle's disease) within one year. Histological examination revealed a defective epidermal differentiation with hyper- and parakeratosis as well as premature keratinization as early as in the epidermal basal cell layer. Studies on lectin binding showed that the glycosylation process was impaired in both the epidermis and the basement membrane zone of the lesional skin. In addition, electron microscopic investigation revealed diabetic microangiopathy of the dermal vessels as well as marked ultrastructural alterations of the dermo-epidermal basal lamina. These findings confirm the association of diabetes mellitus with Kyrle's disease previously described; they make us suggest that Kyrle's disease might be characterized by a defective differentiation of the epidermis and the dermo-epidermal junction--due to some alteration of the underlying glycosylation processes--rather than by a local disorder of keratinization. Regarding the clinical manifestation of the disease, both diabetes mellitus and chronic renal failure may play a part as precipitating factors.