This is a report of three patients with hypohidrotic ectodermal dysplasia, or Christ-Siemens-Touraine syndrome, their genealogic backgrounds and the stereomicroscope and scanning electron microscopic appearances of the hair, the skin of their fingertips and palms as well as skin studies of members of their families. The skin morphology was recorded by means of silicone monomer rubber impressions and epoxy resin dyes. In two of the patients the disease was acquired by X-linked inheritance, while in the third, a boy, it appeared to follow an autosomal dominant pattern. Defects of the skin of the fingertips and palms of the propositi and members of the families included abnormalities of the morphology and pattern of the epidermal ridges, reduction of sweat pores varying from 13 to 87% of normal, and changed anatomy of the openings of the sweat glands. The openings were shallow and with less whorling compared to the normal, funnel-shaped sweat pores. Among the sweat pores, micropores, or openings with an average diameter of 5.3 micrometers, were observed. One of the propositi and the affected father of another had orifices on their fingertips resembling hair sheaths. Two propositi and the affected father of one exhibited grooving of the hair. The findings confirm the necessity for genealogic investigations in patients with or suspected of having the disease in order to advise parents or prospective parents. They also illustrate the usefulness of stereomicroscopy and scanning electron microscopy in observing skin and hair abnormalities.