Symptomatic gastro-intestinal metastasis in lung cancer is extremely rare and only a few case reports have been published. Here, we report a case with lung adenocarcinoma that presented with acute abdominal pain, nausea and vomiting due to duodenum, jejunum, and colon obstruction by the gastro-intestinal metastasis. The patient underwent colonoscopy and the pathologic report was adenocarcinoma. When there are similar histologic findings in both colon and pulmonary lesion, the question is whether both lesions are primary cancer or the colon lesions are metastases from lung cancer. Microscopic examination of a conventional pathologic section was not sufficient to make this determination. Immunohistochemistry was positive for thyroid transcription factor-1 (TTF-1) and cytokeratin 7 (CK7), and negative for cytokeratin 20 (CK20) and caudal-related homeobox transcription factor-2 (CDX-2) on colon mucosa specimen. Accordingly, we used immunohistochemical marker for differential diagnosis of primary adenocarcinoma of the lung with gastro-intestinal metastasis.