Two unrelated families are presented in both of which a child with generalized epidermolytic hyperkeratosis (congenital bullous ichthyosiform erythroderma) had a parent with linear epidermolytic hyperkeratosis (epidermolytic epidermal naevus). Light and electron microscopy of skin biopsies of lesions from the children and parents showed typical epidermolytic hyperkeratosis. Gonadal mosaicism in patients with linear epidermolytic hyperkeratosis may be responsible for transmission of the abnormality to the offspring.