This report describes two infants with recurrent pulmonary edema after umbilical cord blood transplantation (CBT). A 3-month-old boy and a 7-month-old boy with infant acute lymphoblastic leukemia underwent CBT from an unrelated donor in the first complete remission. The conditioning regimen consisted of busulfan, etoposide, and cyclophosphamide. Tacrolimus and short-term methotrexate were administered for the prophylaxis of acute graft-versus-host disease (GVHD). Neutrophil engraftment was achieved on days 17 and 19, respectively. Neither infant developed acute GVHD. They both exhibited tachypnea and weight gain on days 25 and 30, respectively, which were diagnosed as pulmonary edema by chest X rays. The respiratory condition of the patients improved within a few days with the close monitoring of weight changes after the administration of diuretics. However, they suddenly developed dyspnea and pulmonary edema again on days 37 and 59, respectively. Steroid therapy was initiated for both patients. Their respiratory condition again improved quickly after the initiation of steroid therapy. Their symptoms and clinical courses may be classified as a new entity of idiopathic pneumonia syndrome (IPS). Therefore, these cases may represent a new unclassifiable IPS associated with either CBT or infants.