The objective of this study was to assess the cause of failure of bedside barcode identification before blood administration. The bedside check is the most critical step for prevention of mistransfusion. A barcode patient-blood unit identification system was implemented in all inpatient wards, operating rooms and an outpatient haematology unit in July 2002. The transfusion service monitored compliance with bedside barcode identification and checked it at 24 h or 1 h after issuing of blood. If electronic checking was not completed at that time, the transfusion service clarified the cause of failure and indicated the immediate use of the issued blood when it was not yet transfused. From April 2004 to December 2007, a total of 43 068 blood components were transfused without a single mistransfusion and 958 transfusions (2.2%) were performed without electronic checking. The overall compliance rate with bedside barcode identification was 97.8%, and it was 99.5% in the past 6 months. The cause of failure of bedside barcode identification was human error in 811 cases (84.7%), handheld device error in 74 (7.7%), system error in 50 (5.2%) and wristband error in 23 (2.4%). The number of errors leading to failure of bedside barcode identification was decreased for human errors, especially manipulation errors, after initiation of notification at 1 h after issuing of blood. The transfusion service may have an important role in increasing transfusion safety by monitoring compliance with bedside verification and bedside use of issued blood.