Atypical hemolytic uremic syndrome (aHUS) has a high mortality rate if not detected and treated early. While in the past, it was associated with renal failure in children, today, it has become increasingly identified among adults. Due to recent advances in the pathogenesis of aHUS and other major thrombotic microangiopathies (TMA), diagnosing it has become a lot easier. We present a case of a 62-year-old man who was initially thought to have thrombotic thrombocytopenic purpura (TTP), but after further evaluation was diagnosed with aHUS. We will discuss how to distinguish aHUS from other major TMA and the role of eculizumab in the management of aHUS.