Hepatoid adenocarcinoma (HAC) is a rare extrahepatic malignant disease with a histopathologic pattern similar to that of hepatocellular carcinoma (HCC). Most hepatoid carcinomas generate a high level of alpha-fetoprotein (AFP). To date, only 11 cases of HAC in the lung have been reported in the literature. Herein, we report a 44-year-old man with an incidentally-found lung mass accompanied by an elevated serum level of AFP as high as 82,714 ng/mL; the mass was confirmed to be HAC on histopathologic examination via a specimen obtained from percutaneous computed tomography-guided biopsy. The CT scan and ultrasonography of the abdomen revealed no evidence of hepatoma or other intraabdominal abnormalities. The follow-up serum AFP level declined to 28,461 ng/mL after a cycle of chemotherapy and radiotherapy.