Gastrointestinal stromal tumors (GISTs) are the most common GI tract mesenchymal tumors. They mainly occur in the stomach and small intestine, although they are occasionally found in the colon, rectum, esophagus, and appendix. However, tumors showing the same pathological findings as GISTs are also found at sites other than the GI tract. These rare extra-gastrointestinal stromal tumors (EGISTs) are found in the omentum, mesentery, pancreas, retroperitoneum, diaphragm, pleura, abdominal wall, and other intra-abdominal sites. Here, we present two cases of EGISTs arising from the retroperitoneum. A 59-year-old woman was accidentally found to have an abdominal mass, and computerized tomography (CT) imaging showed an intra-abdominal mass with a size of 4.4 X 6.4 cm in the epigastric region of the abdomen, just adjacent to the lesser curvature of the stomach and pancreatic tail. The mass was resected, and pathological results showed an EGIST that stained positive for CD117 (c-kit). The second patient was an 84-year-old man who visited our outpatient clinic with chronic diarrhea and intermittent dyspepsia. An abdominal CT scan showed a hypodense lesion, about 5.2X 8X 5.8 cm in size, in the left upper quadrant of the abdomen, just adjacent to the spleen, stomach, and pancreatic tail. He underwent laparotomy, and EGIST was confirmed using pathological examination. Resection remains the treatment of choice for EGISTs. However, the existing data on EGISTs are not adequate for significant conclusions on prognosis and survival. Therefore, further studies are imperative.