Lung cancer with hereditary angioedema was diagnosed in a 69-year-old man. Laboratory examinations revealed depletion of the fourth component of complement and C1 inhibitor activity. A bone metastasis was present. After the first chemotherapy, acute attacks of edema in the upper chest and the laryngeal mucosa occurred and dyspnea progressed, but these symptoms were immediately improved by administration of C1 inhibitor concentrate. Because of the danger of angioedema that might be expected following chemo-radiotherapy, he was treated with danazol. The patient then showed no sign of an edema attack during therapy for lung cancer.