We present the first reported case of hereditary angioedema (HAE) with gastric involvement to be successfully evaluated by endoscopy both during and after an attack. A 31-year-old man who had a family history of angioedema was admitted to our hospital with complaints of abdominal pain and swelling of extremities. Computed tomography scan and endoscopy carried out during this attack revealed transient gastrointestinal wall edema which, along with decreased levels of serum C4 and C1 inhibitor, confirmed the diagnosis of HAE with gastrointestinal involvement. During the attack, the gastric mucosa was erythematous and edematous, and parts of its surface bulged into the gastric lumen, resembling a submucosal tumor, as a result of massive submucosal edema. During the healing process, a number of small nodules and raised erosions developed over the entire gastric mucosal surface after healing of prominent gastric edema. Within 55 days, the gastric mucosa had returned to normal. The endoscopic findings for the stomach in HAE have not, to our knowledge, been previously described.