[eng] Four cases of BK virus-associated Hemorrhagic Cystitis (HC) in an allogeneic Hematopoietic Stem Cell Transplant (allo-HSCT) setting are reported, including -for the first time- two patients who underwent haploidentical allo- HSCT. Outcome of conventional management was not satisfactory so a novel therapy with Hyperbaric Oxygen Therapy (HBOT) was used. Patients received a median of 35 sessions of HBOT at 2.2 Atmospheres Absolute (ATA) for 90 minutes, 5 days a week in a hyperbaric chamber. After treatment, hematuria was completely resolved without toxicity with a follow-up of between 7 and 36 months. HBOT should be considered as an option in refractory HC after allo- HSCT, including in haploidentical setting.