Thrombotic thrombocytopenic purpura (TTP) is a disease characterized by mechanical anemia with fragmentation of red blood cells and thrombocytopenia by consumption. The physiopathology has been extensively studied and a severe deficiency of ADAMTS 13, proteolytic enzyme of von Willebrand factor (vWF), has been shown to be responsible for its manifestation. We stress the importance of visual blood smear examination when clinical and hematological features of TTP are present, as it seems to be under-diagnosed, especially in infants and young adults. Superpositions with diarrhea-associated hemolytic uremic syndrome (D+ HUS) and atypical HUS (aHUS) are controversely discussed. Henceforth this article proposes a non-exhaustive review of current diagnostic, therapeutic and prognostic features of these diseases.