Gastric metastases from lung adenocarcinoma are rare. Because gastric metastasis grossly resembles advanced gastric cancer, it is difficult to diagnose gastric metastasis especially when the histology of the primary lung cancer is adenocarcinoma. We describe a case of gastric metastasis from primary lung adenocarcinoma mimicking Borrmann type Ⅳ primary gastric cancer. A 68-year-old man with known lung adenocarcinoma with multiple bone metastases had been experiencing progressive epigastric pain and dyspepsia over one year. Esophagogastroduodenoscopy revealed linitis plasticalike lesions in the fundus of the stomach. Pathologic examination revealed a moderately differentiated adenocarcinoma with submucosal infiltration. Positive immunohistochemical staining for thyroid transcription factor-1(TTF-1) and napsin A(Nap-A) confirmed that the metastasis was pulmonary in origin. The patient had been treated with palliative chemotherapy for the lung cancer and had lived for over fifteen months after the diagnosis of gastric metastasis. Clinicians should be aware of the possibility of gastric metastasis in patients with primary lung adenocarcinoma, and additional immunohistochemical staining for Nap-A as well as TTF-1 may help in differentiating its origin. Gastric metastases from lung adenocarcinoma are rare. Because gastric metastasis grossly resembles advanced gastric cancer, it is difficult to diagnose gastric metastasis especially when the histology of the primary lung cancer is adenocarcinoma. We describe a case of gastric metastasis from primary lung adenocarcinoma mimicking Borrmann type Ⅳ primary gastric cancer. A 68-year-old man with known lung adenocarcinoma had multiple excipients had been experiencing progressive epigastric pain and dyspepsia over one year. Pathologic examination revealed a moderately differentiated Adenocarcinoma with submucosal infiltration. Positive immunohistochemical staining for thyroid transcription factor-1 (TTF-1) and napsin A (Nap-A) confirmed that the metastasis was pulmonary in origin. The patient had been treated with palliative chemotherapy for the lung cancer and had lived for over fifteen month s after the diagnosis of gastric metastasis. Clinicians should be aware of the possibility of gastric metastasis in patients with primary lung adenocarcinoma, and additional immunohistochemical staining for Nap-A as well as TTF-1 may help in differentiating its origin.