A 33-year-old man with epigastralgia was admitted. Upper gastrointestinal endoscopy revealed gastric fold hypertrophy, mucosal hemorrhage, and widespread erosion in the stomach and aphthoid erosion in the duodenum. The presence of intranuclear inclusion bodies positively stained with anti-cytomegalovirus antibody from the biopsy specimens indicated that the gastroduodenitis was related to cytomegalovirus (CMV) infection. He recovered within 2 weeks without antiviral therapy. Duodenal involvement of CMV infection is fairly rare in immunocompetent hosts.