A 61 year old man presented with chronic bronchitis, which he had been suffering from for many years, and reported the recent onset of polyuria with polydipsia. A chest X-ray showed a peripheral pulmonary nodule in the right lower lobe, that was diagnosed as small cell lung cancer following histological examination of the pulmonary tissue specimen, obtained with transbronchial biopsy. After establishing the central origin of the diabetes insipidus, its cause was revealed by magnetic resonance imaging of the brain, that demonstrated metastasis to the hypothalamic-neurohypophyseal area.