A primitive neuroectodermal tumor (PNET) belongs to the Ewing's sarcoma family and is a malignant small round cell tumor of neural crest origin. The most common site of an extraosseous Ewing's sarcoma is in the soft tissue of the body and extremities. A PNET in the ovary is uncommon. A PNET in the ovary is most often found with a metastasis and the prognosis is poor. The diagnosis of this tumor is confirmed following a pathohistological examination of tissue obtained after an open biopsy or surgery, but no case of a PNET has been diagnosed by the use of endoscopy in Korea. We present a case of a primitive neuroectodermal tumor of the ovary, which metastasized to the duodenum as diagnosed by use of an endoscopic biopsy in a 32-year-old woman who presented with abdominal discomfort. (Korean J Gastrointest Endosc 2009;38:356-359)