Hemolytic-uremic syndrome (HUS) is the most common cause of acute renal failure in children below 3 years of age. It is defined by a triad of symptoms which associates hemolytic anemia with fragmented erythrocytes, thrombocytopenia and acute renal failure. Three types of HUS can be distinguish: typical HUS, also called diarrhoea-associated (D+HUS), very rare atypical HUS (DHUS) and secondary HUS (drug induced, C+HUS, in patients receiving marrow transplantation, etc.). The common event among these entities appears to be vascular endothelial cell injury, which induces mechanical destruction of erythrocytes, activation of platelet aggregation and local intravascular coagulation, especially in the renal microvasculature. D+HUS represents 90 % of HUS in children. Evidence of exposure to verotoxin (VT), shiga toxin (ST) producing Escherichia coli (VTEC or STEC) has been demonstrated in many countries in about 85 % of cases. Serotype O157:H7 is the most frequent. Early and accurate supportive treatment and early start of dialysis is the major importance and allows a current mortality rate bellow 5 % - 10 %. Vital prognosis is compromized in cases with multivisceral involvement. After 15 years or more of apparent recovery, 20 to 60 % of patients have residual renal symptoms, with up to 20 % having chronic renal insufficiency (CRI) or end-stage renal disease (ESRD). Atypical HUS represents less than 10 % of HUS in children. Some of these cases (familial) are associated with low C3 levels, hereditary deficiency of factor H or with mutations in factor H gene. The deficiency of von Willebrand factor cleaving protease, as reported in adults with thrombotic thrombocytopenic purpura (TTP), is not present in D+HUS.

        Key words: Hemolytic uremic syndrome - Acute renal failure - Verotoxin producing Escherichia coli - Thrombotic thrombocytopenic purpura