Giant gastric ulcers are defined as ulcers with a diameter greater than 3 cm. Previously they have not been described in lung transplant recipients. We report a high incidence of symptomatic giant gastric ulcers and identify the risk factors for ulcer development in these patients. We examined the records of all 95 patients who had undergone lung transplantation at our institution from November 1991 to July 1995. Fourteen of the patients who underwent lung transplantation developed symptoms that required esophagogastroduodenoscopy. Three of these patients (21%) were found to have giant gastric ulcers. The relative risk of giant gastric ulcer in symptomatic patients undergoing endoscopy after lung transplantation is over 40 times that of population controls. The patients who developed giant gastric ulcers, despite H2 antagonist use, had all received bilateral lung transplantation and had received nonsteroidal antiinflammatory drugs, cyclosporine, and high-dose intravenous corticosteroids. The risk of developing giant gastric ulcers is significantly increased in patients who have undergone bilateral orthotopic lung transplantation. Clinicians should be made aware of this complication in order to avoid use of ulcerogenic medications in this population. Avoidance of these medications could potentially minimize the risk of this complication.