Hemorrhagic cystitis (HC) is a major cause of morbidity after allogeneic bo
ne marrow transplantation (BMT). Many therapies have been investigated to p
revent or treat HC, but effective treatment for HC is still limited. While
the efficacy of hyperbaric oxygen therapy has been established for HC due t
o chemotherapy and/or radiation therapy, its role in HC occurring after all
ogeneic BMT has yet to be defined. We report two cases of life-threatening
late-onset HC after allogeneic BMT in children, which resolved after treatm
ent with hyperbaric oxygen.