Hemolytic uremic syndrome (HUS) consists of a triad of microangiopathic hemolytic anemia, thrombocytopenia and renal failure. Atypical hemolytic uremic syndrome (aHUS) is characterized by the absence of antecedent diarrhea, the tendency to relapse, a positive family history and a poor outcome. Autosomal recessive and dominant inheritance have been reported. Precipitating events such as pregnancy, virus-like disease or sepsis are observed in some instances. Intrinsic abnomalities of the complement system have been detected in families with aHUS, like the mutations in complement factor H (FH), membrane cofactor protein (MCP), complement factor I, deficiency in von Willebrand factor cleaving protease (vwf-cp) activity, presence of antifactor- H antibodies, or combinations of mutations for FH and MCP. Hemodialysis, fresh frozen plasma administration or exchange and renal transplantation are used in the treatment. In future, gene therapy may be considered. In this review, the reports from various centers were analyzed. Anahtar Kelimeler : hemolitik üremik sendrom, patogenez, kompleman, tedavi, hemolytic uremic syndrome, pathogenesis, complement, treatment