Hemorrhagic cystitis (HC) following bone marrow transplantation (BMT) develops as a result of urothelial damage. Infection, medication and pelvic irradiation for cancer are the most common causes. The conventional management includes hyperhydration. Bladder irrigation by catheter placement and intravesical alum, prostaglandin F2 or formalin instillation is used in refractory cases. The course of HC may occasionally be associated with significant blood loss and worsened morbidity. We report a case of refractory HC treated successfully with hyperbaric oxygen.