SummaryThe authors report a new case of Thrombotic thrombocytopenic purpura (rapid fatal evolution in a 47 years old female, although treated with prednisone; haematological findings, including serological studies that gave negative results; post-mortem examination confirming the diagnosis). The authors review the pathogenic discussion (on pathological and physio-pathological grounds) about this syndrome, which might be classified, besides collagen diseases and periarteritis nodosa, amongst pathological reactions to hypersensibilization.