This is a case of atypical hemolytic uremic syndrome (HUS) due to invasive pneumococcal disease in which the prominent clinical features were reticulocytopenia and hepatosplenomegaly, leading to the incorrect initial diagnosis of acute leukemia. Delayed diagnosis of HUS, especially in atypical cases, can lead to increased morbidity and mortality. Atypical HUS must be part of the differential diagnosis of children who present with clinical characteristics suggestive of a hematologic malignancy with associated renal injury.