Inherited ichthyoses can be divided into four different clinical types: ichthyosis vulgaris, ichthyosis congenita, ichthyosis hystrix, and atypical ichthyoses. The hereditary transmission is autosomal dominant, recessive, or x-linked. There are some ichthyosiform conditions in which the mode of inheritance is still unknown. Histopathologic studies reveal retention hyperkeratosis in dominant ichthyosis vulgaris and proliferation hyperkeratosis in the congenital ichthyoses. The hystrix-like ichthyoses show partly acanthokeratolytic (epidermolytic) hyperkeratosis and partly proliferation hyperkeratosis. The ultrastructural features of ichthyosis vulgaris and acanthokeratolytic (epidermolytic) hyperkeratosis are discussed.