An 85-year-old woman was admitted to our hospital because of vomiting. An upper gastrointestinal series what showed a large esophageal hiatus hernia, suggesting an association with extrinsic pressure in the middle portion of the stomach. An upper gastrointestinal endoscopic examination showed severe esophagitis and a prominent narrowing in the middle portion of the stomach, however, it showed normal gastric mucosa findings. CT and MRI revealed a large tumor extending from the region of the lower chest to the upper abdomen. From these findings, the tumor was diagnosed as gastrointestinal stromal tumor (GIST), which arose from the gastric wall and complicated with an esophageal hiatus hernia. We performed a laparotomy, however, the tumor showed severe invasion to the circumferential organs. Therefore, we abandoned the excision of the tumor. Histologically, the tumor was composed of spindle shaped cells with marked nuclear atypia and prominent mitosis. The tumor cells were strongly positive for CD34 and c-kit by immunohistochemical examination. From these findings, the tumor was definitely diagnosed as a malignant GIST. As palliative treatment, we implanted a self-expandable metallic stent in the narrow segment of the stomach. The patient could eat solid food and was discharged. In the treatment of esophageal hiatus hernia, the rare association of GIST should be considered.