The pituitary gland and infundibulum can be involved in a variety of medical conditions, including infiltrative diseases, fungal infections, tuberculosis, primary and metastatic tumors. Metastases to the pituitary gland are absolutely rare, and they are generally secondary to pulmonary carcinoma in men and breast carcinoma in women. Pituitary metastases more commonly affect the posterior lobe and the infundibulum than the anterior lobe. The posterior lobe involvement may explain why patients with pituitary metastases frequently present with diabetes insipidus. We are presenting a case report of a 48-year-old male patient with sudden onset of polyuria and persistent thirst. Laboratory results revealed central diabetes insipidus. Computed tomography (CT) scan of the brain showed a mass located in the sella turcica and suprasellar region. CT scan of the chest showed a mass in the right superior lobe with mediastinal lymphadenopathy. Bronchoscopy and biopsy demonstrated a pulmonary adenocarcinoma. Thus, we made a diagnosis of lung cancer with local and pituitary metastases. The patient received radiotherapy on the pituitary gland and adjuvant chemotherapy. As a result the intrasellar and suprasellar mass decreased in size and urinary output accordingly decreased. In conclusion, in patients presenting with sudden onset of diabetes insipidus pituitary metastases should be taken in account in differential diagnosis.