Keratosis follicularis spinulosa decalvans (KFSD) is a rare X-chromosomal disorder. It consists of follicular hyperkeratosis of the skin, scarring alopecia of the scalp, absence of the eyebrows, and corneal degeneration. There is photophobia in childhood, but the symptoms tend to diminish after puberty, and prognosis for vision is good. Some heterozygotes do show clinical symptoms. In a large Dutch pedigree we performed DNA analysis in order to localize the KFSD gene. In 54 individuals, including 21 affected males, RFLP analysis was done using DNA probes covering the X chromosome. Two-point linkage analyses with 19 informative DNA markers revealed significant linkage to DNA probes on Xp21.1-p22.3. The highest lod scores of 5.70 and 4.38 were obtained with DXS41 and DXS16 at a recombination fraction of zero and 4 cM, respectively. Multipoint linkage data place KFSD between DXS16 and DXS269. Our data confirm X linkage of KFSD in this family and tentatively map the gene on Xp22.2-p21.2. Combined with clinical investigation, RFLP analysis may become an important tool in carrier detection.