Choriocarcinoma is an aggressively growing and widely metastasizing tumor that originates from trophoblastic cells. A primary gastric choriocarcinoma (PGC), however, is very rare. A 76-year-old female patient visited the emergency department of Wonkwang University Hospital with abdominal discomfort and melena. Esophagogastroduodenoscopy revealed a huge ulceroinfiltrative mass lesion with blood clots on the boundary between the greater curvature side and the posterior wall side of the stomach lower body. CT showed a 3-cm exophytic mass lesion with heterogeneous enhancement, an ulcer lesion at the posterior wall side of the stomach lower body, and multiple enlarged lymph nodes at the splenic artery and left gastric artery nodal stations. She underwent a radical subtotal gastrectomy with a D2 lymph node dissection. The final diagnosis was PGC coexisting with adenocarcinoma based on the pathology results. This paper reports a rare case of primary gastric choriocarcinoma coexisting with adenocarcinoma and discusses the characteristics of this neoplasm with reference to the literature. (Korean J Gastroenterol 2019;73:350-354)