Langerhans cell histiocytosis (LCH) is a rare illness, and the disease afflicting the thyroid gland is very uncommon, even in the presence of multisystem involvement. In this report, we document histologically, for the first time, concurrent involvement of the thyroid and parathyroid glands by LCH. A young Chinese woman with a history of diabetes insipidus and hypogonadism underwent a total thyroidectomy for enlarged thyroid gland secondary to LCH causing airway obstruction. Microscopic examination of the excised specimen disclosed CD1a- and S-100-positive LCH cells involving the thyroid and parathyroid glands. In a patient with LCH affecting the thyroid gland, parathyroid gland disease should be suspected when the serum calcium levels are depressed in association with an inappropriate serum parathyroid hormone level, such as a normal parathyroid hormone level in this case.