We describe a case of trichothiodystrophy occuring as an isolated disorder. A 19-year old man has had sparse and brittle hair since birth. Physical examination and routine laboratory tests revealed an otherwise healthy man of normal intelligence. Microscopic observation of the hair under polarized light showed typical alternation of bright and dark bands(tiger-tail pattern). Scanning electron microscopy showed trichoshisis(transverse fractures through hair shaft), incomplete or absent cuticles, brush breaks weathering of the hair and trichonodosis. (Korean J Dermatol 2000;38(4)：533~536)