A 23-year-old woman presented with diffuse white hair nodules, hair fragility, and the inability to grow long hair. Examination of specimens under the light microscope showed the morphologic characteristics of trichorrhexis nodosa. Results of tests revealed hypothyroidism. Treatment with a daily dose of 0.1 mg L-thyroxine sodium for six months restored euthyroidism and concurrently normalization of the hair defect was observed. The corrected hair defect observed after replacement therapy may point toward a causal relationship between hypothyroidism and trichorrhexis nodosa. To the best of our knowledge, this is the first report of trichorrhexis nodosa associated with hypothyroidism.