Trichothiodystrophy (TTD) is a rare, autosomal recessive, multisystem disorder characterized by sulfur-deficient brittle hair, growth and mental retardation, and ichthyosis. TTD is caused primarily by mutations in the xeroderma pigmentosum group D (XPD) gene, which encodes a subunit of the basal transcription factor IIH. We have identified a novel heterozygous mutation in XPD (c.1906C>T; p.R636W) resulting in mild-phenotype TTD in the proband and her mother. No identical variations were found in one hundred healthy Korean controls. In silico analysis suggested that the novel mutation was a causative mutation for TTD. This genotype-phenotype correlation provides a unique insight into the TTD inheritance pattern and could prove useful in the diagnosis of patients.