There are several conditions that have the clinical phenotype of the hemolytic uremic syndrome (HUS). This phenotype consists of acute hemolytic anemia with fragmented erythrocytes, thrombocytopenia, and acute renal injury. The Typical or classical from of HUS tends to occur in infants and children, usually in association with an acute episode of bloody diarrhea, may be mild or severe, and frequently has a good prognosis. The commonest cause of this form of HUS is a verotoxin-producing bacterium such as E. coli O157: H7, or a shiga toxin-producing shigella bacterium. This form of HUS cannot be confused easily with thrombotic thrombocytopenic purpura. Recent studies have shown that these patients have very high levels of elastase, and that most of them have a typical pattern of circulating VIII: vwf multimers. There are two groups of Inherited forms of HUS: autosomal recessive and autosomal dominant. These patients tend to have an insidious onset of HUS with either no predisposing cause, or they may have a preceding “viral” infection. The clinical condition is often progressive, and death or end stage renal failure often occur.