A 17-year-old girl presented with polyuria (7 L/day) and polydipsia for one year. Initial urine osmolality was 113mOsm/kg H₂O. Following 6 h of fluid restriction, serum plasma osmolality reached 300mOsm/kg H₂O, whereas urine osmolality was 108mOsm/kg H₂O. Urine osmolality was increased by 427% from 108 to 557mOsm/kg after vasopressin challenge. The patient was diagnosed with central diabetes insipidus, possibly derived from the atypical occupation of a Rathke's cleft cyst at the pituitary stalk following magnetic resonance imaging with enhancement. She was discharged with desmopressin nasal spray (10 µg); urine output was maintained at 2-3 L/day, and urine osmolality was >300 mOsm/kg. Additional pituitary image studies and evaluation of hypopituitarism should be included in the differential diagnosis of patients with central diabetes insipidus.