An 82-year-old man presented with weight loss and lethargy. Thyroid function tests showed a fT4 7.6 pmol/l and TSH 0.08 mU/l. Short synacthen test confirmed hypoadrenalism with baseline cortisol of 34 nmol/l and 30 min sample 156 nmol/l. He had low gonadotrphin levels and Prolactin was 551 μ/l. He was commenced on hydrocortisone and levothyroxine treatment with symptomatic improvement. An urgent CT scan revealed multiple enlarged lymph nodes above and below the diaphragm suggestive of lymphoma. Bone marrow biopsy was normal. MRI of the brain showed a 19×16×16 mm suprasellar mass and a further 1 cm mass in the right cerebellar vermis. Appearances were consistent with malignant disease. His vision deteriorated rapidly within a few weeks and he developed cranial diabetes insipidus with extreme thirst and polyuria. Serum sodium levels rose to 153 mmol/l with serum osmolality of 318 mosm/kg. He was commenced on desmopressin. On review of the scans, his optic nerves were diffusely infiltrated and ballooned by tumour. It was felt that decompression would not improve his vision. Mediastinoscopy with lymph node biopsy confirmed metastatic small cell carcinoma. He was transferred to oncology for palliative radiotherapy and possible chemotherapy. Metastases to the pituitary are uncommon and usually result from breast or bronchial carcinoma. Other causes include lymphoma and gastro-intestinal cancers. Diabetes insipidus is the most common presenting feature as the most common site of metastases is the neurohypophysis. Pituitary metastatic malignancy rarely presents as acute Hypopituitarism and this case highlights a rapidly progressive visual failure and Hypopitutarism. His diabetes insipidus was unmasked by hydrocortisone therapy. Treatment may involve surgery, chemotherapy and radiotherapy. Tumour resection may be difficult and may not improve survival. In one series, median survival was 180 days.