The introduction of a blood component system has made Group O unmatched packed red blood cells (G O UPRBCs) available for emergency resuscitation from hypovolemic shock. A seven-year retrospective review is presented, describing the use of 537 units of G O UPRBCs for the resuscitation of 133 trauma patients. This represented 9.1% of all patients admitted to the Regional Trauma Unit who received blood for resuscitation. Ten of 116 patients on whom further blood bank testing was performed developed positive direct antiglobulin tests (seven of these were demonstrated to be negative 48 hours after transfusion); seven of the ten patients had received more than eight units of G O UPRBCs. No clinical complications were encountered. G O UPRBCs are safe and efficient for emergency resuscitation. Non-group O patients receiving eight or more units of G O UPRBCs should not receive unmatched type-specific blood.