We report a typical case of post-transfusion purpura (PTP) due to anti-PlA1 in a 65-year-old woman. Serological studies were carried out using flow cytometry (FCM). The patient also developed red cell alloantibodies that produced a delayed hemolytic transfusion reaction (DHTR) and broad HLA antibodies. Treatment with high-dose intravenous IgG (HDIgG; a first-generation preparation) was ineffective, but a course of steroids resulted in a rapid increase in the the platelet count.