Although rare, passive transfer of platelet antibodies through blood products can result in thrombocytopenia, acute transfusion reactions, and death. We report a case of severe alloimmune thrombocytopenia from a plasma transfusion. A postliver transplant patient with a normal platelet count received fresh frozen plasma before liver biopsy. Postbiopsy, she developed cardiorespiratory distress, petechiae, and severe thrombocytopenia (platelet count 2000/μL). Her platelet count recovered to normal after 1 week. This diagnosis should be considered whenever an unexpected drop in the platelet count occurs after a plasma-rich transfusion. Conservative transfusion practices and more targeted donor screening may prevent similar events.