The transmission of hepatitis A by blood products has been thought to occur rarely or not at all. By measuring IgM antibody to hepatitis A virus, we diagnosed a case of hepatitis A transmitted by the transfusion of a unit of fresh frozen plasma. Since the commercial availability of methods for measuring IgM antibody to hepatitis A, four other well-defined cases of hepatitis A transmitted by blood products have been reported in the literature. We detail our case and the natural history and importance of this clinical entity.