Atypical hemolytic uremic syndrome (aHUS) is a devastating form of renal thrombotic microangiopathy. In the last five years, we have finally witnessed a dramatic improvement in the management of aHUS patients, and three breakthroughs in our understanding of aHUS have led to such an improvement. The first breakthrough was the emergence of a new clinical picture of aHUS (frequency of adult cases, and overall poor renal prognosis despite plasma therapy). The second breakthrough was the identification of complement alternative pathway dysregulation as a major risk factor for aHUS. The third breakthrough was the availability in clinical practice of the first complement inhibitor, the anti-C5 monoclonal antibody, eculizumab. Available data from case series and prospective studies indicate that eculizumab use has dramatically improved the renal prognosis of aHUS. These breakthroughs have prompted the French working group on aHUS to propose a new algorithm for the management of aHUS in children and in adults. This algorithm will evolve as we gain new insights in the pathogenesis and evolution of aHUS in the eculizumab era.