我們在此報告一個乳癌轉移患者，在接受首次化療後，因發燒而注意到病人有多尿以及多渴之情形。在經過一系列檢查之後診斷為尿崩症，核磁共振檢查後發現腦垂腺轉移，在經過藥物治療以及放射線治療之後，病人尿崩症狀完全受到控制。

Pituitary metastatic disease is rare, accounting for 1% of all excised pituitary tumors and generally involving the posterior pituitary. Neoplasms that more often originated pituitary metastases are breast and lung cancer. We describe a case of a 50-year-old woman, diagnosed with breast cancer with liver and bone metastases, who underwent chemotherapy. During hospitalization, she developed polydipsia, polyuria, and nocturia. She had a large volume of 24-hour urine production (8-10L/day) with a very low urine osmolality (109 mosm/kg) compared to that of the plasma (334 mosm/kg). Further biochemical and hormonal workups were normal except for hypernatremia and hyperprolactinemia. Pituitary MRI showed a contrast-enhanced nodular lesion in the pituitary stalk, suggesting a metastatic lesion. The patient was treated with DDAVP and local radiotherapy, which led to the patient’s clinical improvement. Twelve months after her diagnosis of diabetes insipidus, she died of the metastatic disease. (J Intern Med Taiwan 2017; 28: 252-257)