Post-transfusion purpura (PTP) is a rare, but severe transfusion reaction in which both donor and autologous platelets are sequestered due to immunization against HPA-1a antigens in HPA-1a negative recipients (HPA: human platelet antigens). We describe a patient who developed PTP during induction therapy for acute myeloid leukaemia. The pitfalls, delays in diagnosing and therapy options of this serious transfusion reaction are discussed.