Diabetes insipidus is a heterogeneous condition characterized by polyuria and polydipsia caused by a lack of secretion of vasopressin, its physiological suppression following excessive water intake, or kidney resistance to its action. In many patients, it is caused by the destruction or degeneration of the neurons that originate in the supraoptic and paraventricular nuclei of the hypothalamus. Known causes of these lesions include: germinoma or craniopharyngioma; Langerhans cell histiocytosis and sarcoidosis of the central nervous system; local inflammatory, autoimmune or vascular diseases; trauma following surgery or accident; and, rarely, genetic defects in vasopressin biosynthesis inherited as autosomal dominant or X-linked recessive traits. Thirty to fifty percent of cases are considered idiopathic. Magnetic resonance imaging (MRI) allows identification of the posterior pituitary hyperintensity and of hypothalamic-pituitary abnormalities. Thickening of the pituitary stalk is the second most common finding on MRI scans in several local inflammatory pathologies and autoimmune diseases or germinoma, but it is not specific to any single subtype. A progressive increase in the size of the anterior pituitary gland should alert physicians to the possibility that a germinoma is present, whereas a decrease can suggest the presence of an inflammatory or autoimmune process. Most children with acquired central diabetes insipidus and a thickened pituitary stalk have anterior pituitary hormone deficiencies during follow-up. Biopsy of enlarged pituitary stalk should be reserved for patients with a hypothalamic-pituitary mass and progressive thickening of the pituitary stalk, since spontaneous recovery may occur.