Thrombotic microangiopathies (TMAs) include thrombotic thromobocytopenic purpura and hemolytic uremic syndrome (HUS). Among these conditions, atypical HUS is now recognized to be a disease of alternative complement pathway dysregulation. Eculizumab is a recombinant humanized monoclonal antibody that binds to the complement protein C5 and prevents the cleavage of C5 to C5a and C5b. Eculizumab has been used as a novel treatment for complement-mediated TMA. We present a case of a patient with human immunodeficiency virus infection who developed TMA and was successfully treated with eculizumab. The effect of long-term treatment with this new medication is unknown, and further studies are needed to establish guidelines in the management of this condition.