A 20-year-old man was admitted to our hospital because of abdominal expansion and vomiting. Abdominal X-ray and computed tomography (CT) scan disclosed massive air with fluid retention in the stomach. After extraction of gastric air and contents by a gastric tube, shock occurred with progression of anemia and multiple organ failure including acute renal failure. Gastroduodenoscopy demonstrated widespread gastric mucosal necrosis without gastroduodenal stenosis, a finding of mucosal necrosis induced by acute gastric dilatation. Because of his poor condition, total gastrectomy was not performed. Continuous hemodiafiltration (CHDF) was started, and blood transfusion and administration of total parenteral nutrition as well as H₂ blocker were done. He recovered from shock and showed improvements of multiple organ failure, gastric dilatation and mucosal necrosis. Although most reported cases of acute gastric dilatation with continuing hemorrhage require surgical treatment, the present case was successfully treated with conservative treatment. Especially, CHDF was effective probably by removing toxic factors including cytokines.