Disseminated superficial porokeratosis (DSP) is an autosomal dominant epidermal keratinization disorder. The genetic basis for DSP has not been clearly elucidated. We previously mapped the locus for DSP to a large region (5.7 Mb) at 18p11.3 in a four-generation Chinese family with DSP, but no gene responsible for porokeratosis has been identified to date. To narrow the critical region for DSP, thereby facilitating the identification of this disease gene and possibly leading to an understanding of the pathogenesis of porokeratosis, genotyping was performed on the same Chinese family with DSP using nine heterozygous single-nucleotide polymorphism markers at 18p11.3. We found the locus of DSP to be located within a 2.7 Mb region between markers rs58085394 and rs238533. Our study provides a map location for isolation of a gene causing DSP.