SUMMARY: Langerhans cell histiocytosis (LCH), a monoclonal disease of histiocytes, may involve several organ systems but rarely primarily involves the thyroid gland. This report presents an extremely rare case of LCH of the thyroid and lungs in a 3-year-old boy who presented with a neck mass for several weeks. The patient subsequently underwent chemotherapy with resolution of the goiter and lung findings, and the patient remained in complete remission 1 year after chemotherapy. LCH of the thyroid should be considered in the differential diagnosis of a child with a thyroid mass. Pulmonary examination should be done in these patients.