A 55-year-old man with advanced myelodysplastic syndrome was hospitalized prior to undergoing an allogeneic bone marrow transplantation. Immediately before hospitalization, he had suffered from phlegmon in both lower extremities and right forearm as well as genital and oral ulcers. After admission, he developed an esophageal ulcer and was thus diagnosed as having intestinal tract-type Behçet disease. HLA-B51 was not present. Within a month, he died of pulmonary hemorrhage associated with pneumonia, possibly because of a low platelet count, and vasculoendothelial damage related to Behçet disease. This is a rare case of myelodysplastic syndrome that developed Behçet disease with a severe esophageal ulcer.