Fourteen monogenic cutaneous disorders of man are compared to similar gene defects in animals. The traits are classified into two groups. In the first group, an identity (homology) of the underlying gene defects is likely. This group includes oculo-cutaneous albinism, Chédiak-Higashi syndrome, aplasia cutis congenita, Ehlers-Danlos syndrome (type I), hypohidrotic ectodermal dysplasia of the Christ-Siemens-Touraine type, X-linked dominant chondrodysplasia punctata, ichthyosis congenita gravis, Menkes syndrome, erythropoetic porphyria, porphyria cutanea tarda, and acrodermatitis enteropathica. In the second group, the traits are similar but the question of their homology cannot be settled. It includes alopecia congenita, hidrotic ectodermal dysplasia of the Clouston type, and hereditary lymphedema. The existence of identical mutations in man and animals provides evidence for the close relationship between the various mammalian species. Homologous traits affecting the skin are of practical importance since the use of these animal models may help to answer those questions which cannot be answered by performing research in human patients.