We retrospectively analyzed the cases of 14 patients (9 women, 5 men, mean age: 51.6 years) with cytomegalovirus (CMV) involvement in the esophagus, stomach, and/or duodenum diagnosed at a single center, to determine their endoscopic features and clinical backgrounds. Thirteen patients (92.9%) had hematologic disease; the other had rheumatoid arthritis. Of the former, 12 patients underwent allogeneic hematopoietic stem cell transplantation, and 9 of these patients had graft-versus-host disease (GVHD) before undergoing esophagogastroduodenoscopy (EGD). All 14 patients had been taking one or more immunosuppressive agents including cyclosporine (n=10), corticosteroids (n= 9), mycophenolic acid (n= 6), tacrolimus (n=3), and methotrexate (n=1). Tests for CMV antigenemia were positive in 11 patients (78.6%). EGD examinations revealed esophageal (n=3), gastric (n=9), and duodenal involvement (n=6). Macroscopically, esophageal lesions by CMV infection presented as redness (n=1), erosions (n=1), and ulcers (n=1). Gastric lesions manifested as redness (n=7), erosions (n=3), exfoliated mucosa (n=2), and verrucous erosions (n=1). Mucosal appearances in the duodenum varied: redness (n=2), ulcers (n=2), multiple erosions (n=2), single erosion (n=1), edema (n=1). CMV was detected even in the intact duodenal mucosa (n=1). In conclusion, physicians must recall the relevance of CMV infection when any mucosal alterations exist in the upper gastrointestinal tract of immunosuppressed patients.