A gastric neuroendocrine carcinoma is very rare, and the histological diagnosis is very difficult. These carcinomas result in a poor prognosis because they are preceded by severe lymphovascular invasion and early metastasis. In particular, it is difficult to distinguish between adenocarcinoma and neuroendocrine carcinoma by endoscopy when no specific symptoms are present (e.g., dyspepsia, nausea). According to published articles in Korea, most cases were diagnosed as adenocarcinoma initially; however, they were confirmed postoperatively as neuroendocrine carcinoma based on a histological examination using immunohistochemical staining. A case of a 55-year-old man, who had an incidental finding of a subepithelial tumor during his health check-up, was recommended for an endoscopic submucosal dissection (ESD). But the patient was lost to follow-up for 4 years. When he was examined again, the size of the tumor had increased from the previous exam. He underwent ESD and was diagnosed with a well-differentiated neuroendocrine carcinoma. (Korean J Gastrointest Endosc 2011;42:236-240)