We sought to investigate a novel mutation in the keratin genes assumed to be responsible for a familial case of oral white sponge nevus. The affected family consisted of a 36-year-old woman, her 17-year-old daughter, and her 14-year-old son. Keratin 4 and 13 genes extracted from venous blood lymphocytes were amplified by using the polymerase chain reaction and directly sequenced. Sequencing analysis of the 3 patients revealed the presence of a novel heterozygous T-to-C transition mutation in exon 1 of the keratin 13 gene, with no abnormalities detected in the keratin 4 gene. We identified a novel heterozygous missense mutation at 332T>C in the keratin 13 gene believed to be related to the development of white sponge nevus.