Tumor metastasis to the pituitary gland has been infrequently reported, and this is probably because only a small proportion of these patients are symptomatic. Most of the symptoms of this malady are related to diabetes insipidus. A 78-year-old man was diagnosed 2 years previously with stage IIIA adenocarcinoma of the lung and treated with sequential chemoradiation therapy and later with whole-brain radiation therapy because of newly developed brain metastasis; he was then admitted to our hospital with symptoms of polydipsia and polyuria. He was confirmed to have central diabetes insipidus that was caused by the pituitary metastasis from lung cancer. His symptoms resolved after treatment with desmopressin. Because of the rarity of this manifestation in lung cancer patients, we report on this case along with a brief review of the relevant literature.