Prenatal diagnosis of X-linked hypohidrotic ectodermal dysplasia was previously performed by the direct histological analysis of fetal skin obtained by late second trimester fetoscopy. The recent gene mapping of the locus for the disorder to the region of Xq11-21.1 now permits the indirect prenatal diagnosis of the disorder by the method of linkage analysis, based on closely linked marker loci, during the first trimester of pregnancy. We report the prenatal diagnosis of a male fetus with a high probability of the disorder by a linkage analysis utilizing restriction fragment length polymorphisms at the DXS159, PGK1, and DXS72 loci, from a DNA sample obtained by a chorionic villus biopsy at 9 weeks gestation. After further counseling, the pregnancy was terminated but the diagnosis could not be confirmed by histological analysis, even though analysis of skin samples by light and electron microscopy showed lack of hair germs, primary dermal ridges, and sweat gland primordia, due to the early developmental stage of the fetus. The use of DNA-based linkage analysis now offers the opportunity for an earlier diagnosis of X-linked hypohidrotic ectodermal dysplasia by a method other than fetal skin sampling. However, families must also fully understand the present limitations of the method prior to undertaking the procedure.