Hemolytic-uremic syndrome (HUS) is a disease characterized by a triad of hemolytic anemia (anemia caused by destruction of red blood cells), acute kidney failure (uremia), and a low platelet count (thrombocytopenia). It predominantly, but not exclusively, affects children. Most cases are preceded by an episode of infectious, sometimes bloody, diarrhea acquired as a foodborne illness or from a contaminated water supply caused by E. coli O157:H7, other non-O157:H7 E. coli serotypes, Shigella, and Campylobacter. A variety of viruses have also been implicated as a causative agent. It is now the most common cause of acquired acute renal failure in childhood. It is a medical emergency and carries a 5–10% mortality rate; of the remainder, the majority recover without major consequences, approximately 30% have residual renal injury. The primary target appears to be the vascular endothelial cell. This may explain the pathogenesis of HUS, in which a characteristic renal lesion is capillary microangiopathy.