A 68-year-old man was referred to our hospital for further examination of a gingival mass. Chest radiographs and magnetic resonance imaging disclosed a bulky mass originating in the upper portion of the left lung, in contact with a chronic empyema lesion that first occurred after resection for pulmonary tuberculosis. Examination of a specimen obtained by percutaneous needle biopsy of the mass led to the diagnosis of large-cell carcinoma. Laboratory findings on admission showed marked leukocytosis (48,100/microliter) without evidence of severe a bacterial infection. The level of G-CSF in serum was abnormally high (246 pg/ml, normal value: < 30 pg/ml). Chemotherapy with vindesine, ifosfamide, and cisplatin resulted in shrinkage of the gingival mass, and a decrease in the G-CSF level to 66 pg/ml. Immunohistochemical staining with an anti-G-CSF monoclonal antibody to the primary lung tumor and the gingival mass obtained at autopsy was positive for cytoplasmic G-CSF.