We describe a new case of isolated trichothiodystrophy. This entity is characterized by sparse and brittle hair, low sulfur hair content, tiger tail pattern of the hair under polarizing microscopy, clean transverse fractures through the hair shaft and absent or defective hair cuticles. To our knowledge there are only two reported cases of isolated trichothiodystrophy without associated additional ectodermal or neuroectodermal dysplasias. Polarized microscopy of cut hair showed transverse fracture points (trichoschisis) and alternating dark and bright bands. Low sulfur content of the hairs was confirmed by amino acid analysis. Many acronyms and eponyms have been created to describe sulfur-deficient brittle hair associated with neuroectodermal abnormalities, leading to confusion. We suggest to use a simple classification scheme, according to increasing severity of associated features as proposed by Van Neste.