Thyroid involvement with Langerhans cell histiocytosis (LCH) is very rare. We report here the case of a 15-year-old female patient with LCH affecting the thyroid gland. She was referred to the department of pediatric endocrinology for secondary amenorrhea. Prior to the diagnosis of LCH, the patient had symptoms of diabetes insipidus (DI) and amenorrhea. The mean time from symptom onset to diagnosis was 2 years. On physical examination the patient had grade 2 goiter, and ultrasound showed bilateral multiple hypoechoic nodules and thyroid heterogeneity. Biochemical analysis indicated central diabetes insipidus and panhypopituitarism. Magnetic resonance imaging (MRI) demonstrated a mass lesion involving the hypothalamus, which appeared iso- to hypo-intense on T2-weighted images and had an intense postcontrast enhancement on T1-weighted images. Nodular goiter coinciding with a hypothalamic mass suggested LCH, and an excisional biopsy was performed. Histological evaluation of the thyroid gland revealed extensive involvement by LCH, and this was confirmed by immunohistochemical analysis showing S-100 protein and CD1a positive Langerhans cells that were weakly positive for CD68. LCH should be considered in the differential diagnosis of a diffusely enlarged firm and irregular thyroid gland and posterior or anterior pituitary dysfunction.