Each year, approximately 9 million platelet-unit concentrates are transfused in the United States; an estimated one in 1,000-3,000 platelet units are contaminated with bacteria, resulting in transfusion-associated sepsis in many recipients. To reduce this risk, AABB (formerly the American Association of Blood Banks) adopted a new standard on March 1, 2004, that requires member blood banks and transfusion services to implement measures to detect and limit bacterial contamination in all platelet components. This report summarizes two fatal cases of transfusion-associated sepsis in platelet recipients in 2004 and describes results of a 2004 survey of infectious-disease consultants regarding their knowledge of transfusion-associated bacterial infections and the new AABB standard. Health-care providers should be aware of the new standard and the need for bacterial testing of platelets to improve transfusion safety. However, health-care providers also should be able to diagnose transfusion-associated infections, because even when testing complies with the new standard, false negatives can occur and fatal bacterial sepsis can result.