SummaryTwo adult cases with the hemolytic uremic syndrome are reported. The first patient died and this illustrates the often bad prognosis of this disease in the adult. The simultaneous occurrence of the familial and recurrent variant of this syndrome in the second patient is highly remarkable. The differential diagnosis with for example thrombotic thrombocytopenic purpura is discussed. A high antibody titer against Coxsackie B, virus was measured in the serum of our first patient, while a rise in antibody titer for mononucleosis infectiosa was observed in the second patient. The role of viral infections, of intravascular coagulation and of immunological phenomena in the pathogenesis of the hemolytic uremic syndrome and the therapy with heparin and platelet inhibitors arc discussed.