Human parvovirus B19 is linked with a broadening spectrum of hematologic disorders, including aplastic crises in the context of hemolytic anemias, neutropenia, thrombocytopenia, and hemophagocytic syndromes. Children with any of these cytopenias should be screened for the presence of B19 because treatment with intravenous gamma globulin may provide resolution of abnormal blood counts if other therapeutic options, such as transfusion, are not adequate or desired.