Norwegian scabies is a rare clinical variant of human infestation with Sarcoptes scabiei var. hominis. It is characterized by hyperkeratotic lesions of the palmar and plantar surfaces, scalp and ears which contain myriad mites. The authors have observed three cases: the first occurred in a old delibited woman with a Recklinghausen's disease, the second in a boy with Down's syndrome, the last in a child treated with immunosuppressors. Review of the literature and study of etiological grounds. The pathogenesis is yet unclear but the altered host factors appear to be the principal determinant: primary or secondary specific immunologic deficit and inability to eliminate the mites because of the absence of scratching, hereditary predisposition to keratotic reaction of the skin.