Papillon–Lefèvre syndrome (PLS) is a rare autosomal recessive disorder of keratinization caused by homozygous mutations in the gene encoding lysosomal protease cathepsin C (CTSC). It is clinically characterized by transgredient palmoplantar keratoderma (PPK) and periodontitis. A 15-year-old boy presenting with PPK from the age of 6 months and late-onset periodontitis that began at the age of 12 years is described. Mutation analysis revealed a homozygous nonsense mutation (p.Y304X) in exon 7 of the CTSC gene. Late-onset periodontitis in a patient with Papillon-Lefèvre syndrome is a rare phenotypic variation.