Hemolytic uremic syndrome (HUS) is a rare disease with a triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Several genetic and acquired abnormalities leading to abnormal activation of the alternative pathway of complement have been identified in patients with atypical HUS (aHUS). Studies over the past decade have shown that the risk of post-transplant recurrence of aHUS depends on the underlying genetic abnormality. The risk is high in patients with mutations in genes (CFH, CFI, C3, CFB) encoding circulating complement proteins and regulators, while patients with mutations in membrane cofactor protein (MCP) and diacylglycerol kinase ɛ (DGKE) generally show good transplant outcome. Recent data provided evidence about the efficacy of the anti-C5 monoclonal antibody Eculizumab in the prevention and treatment of post-transplant aHUS recurrences.