We report the rare case of an elderly patient with an advanced gastric cancer arising from an upside-down stomach through a paraesophageal hiatal hernia (PEH). An 82-year-old man presented with appetite loss and anemia. Upper gastrointestinal endoscopy revealed a type 1 tumor located in the middle body of the stomach. An upper gastrointestinal series and computed tomography showed organoaxial rotation of the stomach, which was located in the mediastinum, through a PEH, indicating an upside-down stomach. The preoperative diagnosis was gastric cancer arising from an upside-down stomach through a PEH. The patient underwent total gastrectomy with lymph node dissection and closure of the hernial orifice. Although a large PEH is a chronic disorder, gastric malignancies should be considered in patients with PEH manifested as an upside-down stomach due to its anatomical characteristics, and careful preoperative diagnosis is mandatory.