摘要Ewing's sarcoma (ES) is a neoplasm of undifferentiated small round cells, which occurs in the bones and deep soft tissues of children and adolescents. We present a rare case of a 44-year-old woman with gastric ES presenting with epigastric pain and weight loss. Ultrasound and computed tomography scans indicated a solid/cystic mass in the pancreatic tail. At laparotomy, the tumor was found attached to the posterior surface of the stomach, completely free from the pancreas, with no lymphadenopathy or local metastases. The polynodal, partly pseudocystic, dark-red soft tumor was excised. Histopathology revealed an anaplastic small-round-cell tumor with strong membranous CD99 immunoexpression. Additionally, there was patchy immunostaining for S-100 protein, vimentin, protein gene product (PGP) 9.5 and neuron-specific enolase, and weak focal CD117 cytoplasmic immunoreactivity. The patient had no adjuvant chemotherapy; her postoperative recovery was uneventful, and she remains symptom-free, and without any sign of recurrence at 20 mo. To the best of our knowledge, this is only the third ever case of gastric ES.