AVP and diabetes insipidus: This case also highlights that treating DI with antidiuretic hormone (ADH) replacement was complicated by extreme difficulties in attaining satisfactory sodium and water balance during the clinical course, with the possibility of coexistent DI and syndrome of inappropriate ADH secretion because of the underlying lung cancer.<h4>Learning points</h4>When patients present with pituitary mass and diabetes insipidus (DI), pituitary metastasis should be considered as an initial differential diagnosis.