We describe four patients with congenital follicular hyperkeratosis, of whom three also had pseudoacanthosis nigricans and two had facial abnormalities. Skin specimens were studied by light microscopy, autoradiography, histochemistry and scanning electron microscopy, and the results were compared with those from patients with keratosis pilaris. The condition appears to constitute a distinctive form of ichthyosis in which the abnormal epidermal differentiation occurs mainly within the hair follicles.