Of 49 patients with trichorrhexis nodosa (TN), 26 had scalp hair involvement, and 20 of these had excessively traumatized their hair. Twenty-three patients had genito-inguinocrural or multiple site involvement and all had pruritus in these areas. In many the TN cleared with less traumatic hair care or with control of the pruritus. Chromatography of urine for argininosuccinic acid and fluorescent acridine orange microscopy and amino acid analysis of hair do not support the theory that this hair abnormality is a metabolic defect. Our clinical findings emphasize the importance of trauma, supported by our recent in vitro reproduction of TN by mechanical stress. The fracturing of hair seen with TN is a common cause of unexplained hair loss.