Ten autopsy and 2 biopsy cases of cytomegalovirus (CMV) infection of the alimentary tract were studied. CMV infection was microscopically determined by the presence of cytomegalic inclusion as well as by the immunofluorescent method. Clinical manifestations such as abdominal pain, diarrhea, hematemesis, bloody stool, perforation, and/or abdominal distension with paralytic ileus were observed in 8 autopsy cases and 1 biopsy case. Disappearance of cytomegalic cells was confirmed by the follow-up study in the biopsy cases. Macroscopically, mucosal hemorrhage or ulceration was found in the gastrointestinal tract from the esophagus to the colon. Ulceration showed a characteristic well-defined punched-out appearance. The esophagus was the most frequently involved organ. However, no cytomegalic cells were found in the squamous epithelium. In the stomach, regenerated epithelial cells were frequently involved in the deeper part of glands. Numerous endothelial cells transformed into cytomegalic cells in the mucosa surrounding the ulcer in the esophagus, stomach, and intestine. Ischemia caused by cytomegalic changes of vascular endothelial cells is thought to play an important role in the pathogenesis of the ulcer of the gastrointestinal tract.