Poorly differentiated neuroendocrine carcinomas (NECs) originating from the gastrointestinal (GI) tract are rare and very highly malignant disease with a poor prognosis. Poorly differentiated NECs most commonly arise in the esophagus and the large bowel; however, they may occur within virtually any portion of the GI tract. It is known, however, that they do not typically occur in the small intestine.A 21-year-old woman visited an emergency room with acute abdominal pain that commenced 2 days prior to her presentation. Thereafter, a computed tomography (CT) scan was notable for a small-intestine perforation, and huge masses were observed in the small intestine and the mesentery. The mass that was located at the ileum site is approximately 100 cm above the ileocecal (IC) valve, and while it is located on the anti-mesenteric border and it seems that luminal narrowing had occurred, an obstruction is absent. Also, a same-nature mass is on the mesentery. The pathologic reports confirmed a small-cell-type NEC with a mass size of 7.5 × 6.5 cm. The mitotic count is up to 24/10 high-power fields (HPFs), the results of the immunohistochemical stain are positive for CD56 and synaptophysin, and the Ki-67 level is 50%. %. After the operation, she was treated with Etoposide-Cisplatin (EP) chemotheraphy. Stable disease was seen during Etoposide-Cisplatin chemotheraphy. Liver metastasis was also confirmed after chemotheraphy. Additionally, Irinotecan and cisplatin were used for 3 cycles, but progression of disease, neutropenic fever, thrombocytopenia, general weakness persisted. Eventually, she died 1 year and 6 months after surgery.Ileum-located NECs are diagnosed very rarely. The most common locations for these tumors along the GI tract are the esophagus and the large intestine, but they can arise anywhere. The prognosis for NECs is poor due to the metastatic disease of most patients at the time of diagnosis. The role of adjuvant treatment requires further evaluation for the attainment of a better understanding of the overall treatment effect.