Thrombotic thrombocytopenic purpura (TTP) is a rare microangiopathic disorder with high morbidity and significant mortality. The primary form of TTP is caused by severe deficiency, acquired or hereditary, of the von Willebrand factor cleaving protease (VWF-CP), ADAMTS-13. Because TTP occurs less frequently in children, general pediatricians are not well informed about the spectrum of clinical symptoms and altered laboratory values, increasing the risk of nondiagnosis and possible fatal outcome. If renal involvement is present, the condition can easily be misdiagnosed as hemolytic-uremic syndrome (HUS). We present a case series of children with severe VWF-CP deficiency with emphasis on the clinical heterogeneity responsible for misdiagnosis and inappropriate treatment. The inherited form may involve onset of symptoms ranging from isolated thrombocytopenia to the full clinical picture characteristic of classical TTP. The most common assumed diagnoses of oligosymptomatic forms are immune thrombocytopenia (ITP) and Evans syndrome, respectively. Accordingly, this article is directed towards pediatricians on neonatal and intensive care units, as well as their colleagues specializing in nephrology, hematology, and neurology.