A 76-year-old man, who had underwent radiation for laryngeal cancer 5 years before, was pointed out abnormal pulmonary lesion on computed tomography. The 4.6 cm-sized lesion was seen in the upper lobe of the left lung. Endoscopic brushing cytology revealed adenocarcinoma. The patient was diagnosed as primary lung cancer of T2N0M0, clinical stage IB. Preoperative serum CA19-9 was elevated to 250 U/ml, although other tumor markers were within normal limits. The patient underwent left upper lobectomy with mediastinal lymph node dissection. Histologically, the lesion was diagnosed as well differentiated adenocarcinoma, mucinous subtype of bronchioloalveolar carcinoma (BAC) in World Health Organization (WHO) classification. Immunohistochemistry shows positive for CA19-9 and thyroid transcription factor-1 (TTF-1).