The purpose of this multicenter study was to assess the incidence and the treatment of hemorrhagic cystitis (HC) in 1218 pediatric patients, with a mean age of 10.8 years, who underwent hematopoietic stem cell transplantation (HSCT). In all, 44 patients (3.6%) developed HC a median 23 days after HSCT. The incidence of HC was higher in allogeneic than in autologous HSCT recipients (P=0.0001). Of the 44 patients, 37 (84%) recovered from HC in a median 30 days (range 3-100); the other seven children died while still suffering from HC. Hyperbaric oxygen therapy (HOT) achieved significantly better results than prostaglandin therapy (P=0.02) in the treatment of grade II-III HC. By multivariate analysis, age <96 months and allogeneic HSCT were significantly associated with the occurrence of HC: P=0.008 and 0.013, respectively. After a median follow-up of 5.75 years, the 5-year survival of patients who did or did not develop HC was: 43 vs 52%, P=0.03, respectively. This study indicates that age and type of HSCT are factors predisposing to HC in children given HSCT and demonstrates the promising role of HOT in a conservative approach to HC treatment.