Science and Education Publishing American Journal of Medical Sciences and Medicine 2327-6657 2 5 2014 09 21 BK Virus in Allogeneic and Autologous Bone Marrow Transplantation: Review Article 85 88 EN Ilhami BERBER Department of Hematology, Bone Marrow Transplantation Unit, Faculty of Medicine, Inonu University, Malatya, Turkey Mehmet Ali ERKURT Funda YETKIN Irfan KUKU Emin KAYA Emin BODAKCI Mustafa KOROGLU Ilknur NIZAM AJMSM2014251 10.12691/ajmsm-2-5-1 2014 09 10 2014 09 17 2014 09 21 The BK virus is a member of the polyomavirus family. When the immune system is compromised, as in patients undergoing chemotherapy after hematopoietic stem cell and solid organ transplantation, the virus is reactivated, leading to haemorrhagic cystitis. While the BK virus is one of the most common causes of morbidity and mortality in patients after allogeneic stem cell transplantation, it rarely occurs after autologous stem cell transplantation. The early diagnosis and treatment of viral cystitis may prevent significant morbidity and mortality associated with haemorrhagic cystitis caused by the BK virus. It is not entirely clear how the BK virus affects prognosis in patients undergoing allogeneic and autologous hematopoietic stem cell transplantation.