Objectives: Patients undergoing bone marrow transplantation are at risk forhemorrhagic cystitis despite appropriate preventive measures. This complication could have an impact on patient survival and other outcome variables. Methods: A retrospective study of patients subjected to bone marrow transplantationwas conducted to determine risk factors for hemorrhagic cystitis and evaluate the impact of hemorrhagic cystitis on certain outcome variables. Patients who experienced hemorrhagic cystitis received various forms of therapy, at the discretion of the treating physician. Results: Hemorrhagic cystitis occurred more frequently in younger patients and those undergoing allogeneic transplantation. The occurrence of hemorrhagic cystitis was associated with increased hospital costs, length of hospitalization, and mortality. Gender, race, type of malignancy, other pretransplantation comorbidity, and the occurrence of other peritransplantation complications were not associated with occurrence of hemorrhagic cystitis. Conclusions: Hemorrhagic cystitis is a significant complication of bone marrow transplantation,which influences economic and survival outcome. Since the number of bone marrow transplants being performed is increasing, urologists should be prepared to play an active role in treating patients who experience this complication. © 1994.