Langerhans cell histiocytosis can cause central diabetes insipidus. Here, a case of Langerhans cell histiocytosis invading the pituitary stalk was experienced. The patient was 15 years old boy, with complaint of polydipsia and polyuria. A water deprivation test was carried out, and the urine osmolarity was increased from 165 to 469 mosm/kg following an injection of AVP to confirm the diagnosis of central diabetes insipidus. A pituitary function stimulation test gave a normal response. A sellar MRI was performed, which showed a thickened pituitary stalk mass (about 5.7mm), with an increased size, 6.9 mm, on a second MRI 2 month later. A tissue biopsy was performed, which showed aggregates of histiocytes and inflammatory cells, with prominent eosinophils (H&E), and also revealed strong reactivity to anti-CD1a antibody on the immunohistochemistry. After confirmative tissue diagnosis, the patient received radiotherapy (900 cGy). The thickened mass of the pituitary stalk disappeared on the MRI following the radiotherapy. The patient was managed with DDAVP nasal spray, after which the polyuric symptoms were completely relieved.