Abstract Blood transfusion has been widely studied and the risk/benefit ratio remains unclear. Focus historically has been upon viral transmission, particularly hepatitis and HIV. Today, with advanced screening for these viruses, the risk for such transmission has become vanishingly small. Immunosuppression, with consequent postoperative bacterial infection and ABO incompatibility are now risks that physicians should consider as associated with allogeneic blood transfusion. Other inflammatory events, such as transfusion associated acute lung injury, also occur. The benefits of transfusion have never been well studied and there is scant literature on that area. Therefore, in an evidence-based medical practice the physician should regard transfusion with a skewed risk/benefit ratio. The following article examines that risk/benefit ratio in the post-AIDS era.