en Pediatric Hematology & Oncology Pediatric Hematology & Oncology گزارش مورد Case report BK virus-associated hemorrhagic cystitis (HC) is frequent in patients undergoing bone marrow transplantation, but it rarely occurs among other immunosuppressed patients particularly in those who are receiving chemotherapy for hematologic malignancies. Herein, we report three children with malignancies suffering from hemorrhagic cystitis due to BK virus infection who were successfully improved.<br> Early detection of BK virus using RT-PCR technique was undertaken. With administration of antiviral agents; specifically, IVIG or leflunomide, BK virus-associated HC could be successfully managed in children affected by malignancies and consequently, chemotherapy of underlying disorder might be continued after virus elimination. BK virus, Cystitis hemorrhagic, Leflunomide, Immunosuppression 33 35 http://ijbc.ir/browse.php?a_code=A-10-405-1&slc_lang=en&sid=1 Shahla Ansari Damavandi shahladamavandi@yahoo.com 10031947532846004645 10031947532846004645 No Department of Hematology-Oncology, Ali Asghar Children's Hospital, Iran University of Medical Sciences, Tehran, IR Neda Ashayeri neda_ashayeri@yahoo.com 10031947532846004646 10031947532846004646 Yes Department of Hematology-Oncology, Ali Asghar Children's Hospital, Iran University of Medical Sciences, Tehran, IR