Abstract Anti-At a is a rare alloantibody that can be clinically significant. We report a case of a woman who, after emergency-released uncrossmatched red blood cell transfusion, experienced an acute hemolytic transfusion reaction attributed to anti-At a . The case presented herein highlights the importance of recognizing that anti-At a may indeed cause acute hemolytic reactions. Immunohematology 2016;32:140–142.