Objective:To analyze the clinical materials of 2 patients with lung cancer complicated with syndrome of inappropriate secretion of antidiuretic hormone (SIADH),and to improve the clinical awareness and management.Methods:One patient was treated with lung cancer chemotherapy alone for 7 courses.The other patient received the strictly limited for liquid intake and tolvaptan by oral against hyponatremia without chemotherapy.Results:With the relapsing and advancing of lung cancer,the hyponatremia and its relevant symptoms of the first patient were poorly relieved.While the level of serum sodium of the second patient returned to the normal level 3 d after administration of tolvaptan.Conclusion:About one-third of the patients with hyponatremia have SIADH.The etiological treatment and symptomatic therapy of hyponatremia should be given to the patients in clinical treatment.