We have experienced a very rare case of hepatoid adenocarcinoma in the lung. A 55-year-old male with a history of smoking was diagnosed as adenocarcinoma of the right S2, and underwent resection of the right upper lobe and dissection of the hilum and mediastinal lymph nodes (complete resection). Pathological examination revealed cuboid atypical cells arranged in a papillary or trabecular fashion, and a proliferating pattern in most part of the tumor resembling that of hepatocellular carcinoma. Immunohistochemistry study showed alpha-fetoprotein (AFP)-positive tumor cells, hence the diagnosis of hepatoid adenocarcinoma was confirmed. Postoperative pathological staging classified the patient as having as p-T2NOMO, p-stage I B disease. The serum AFP level was not determined before surgery, but the value decreased gradually after surgery and has since remained within the normal range. At present, 32 months after the operation, no signs of recurrence have been observed. Hepatoid adenocarcinoma in the lung has been reported in eight patients with the present one being the ninth case. All were males, the tumor diameter was large and the patient prognoses were mostly poor, but at early stage two cases of long-term survival have been reported indicating that the stage is the most important prognostic factor also for rare tumor.