A 17-month-old boy in whom immune-mediated thrombocytopenia (ITP) was the presenting manifestation of infection with human immunodeficiency virus (HIV) is being successfully managed with intermittent high-dose intravenous gamma globulin (IVIG) allowing maintenance of hemostatic platelet counts while avoiding the immunosuppression associated with other therapeutic modalities used to treat ITP. He continues to demonstrate marked responsiveness to IVIG, and has been maintained on weekly or bimonthly infusions for 12 months. The serendipitous documentation of HIV infection prior to IVIG therapy for immune-mediated thrombocytopenia in this child documents the importance of HIV testing prior to IVIG therapy to prevent erroneous assignment of IVIG as the vehicle responsible for transmission of HIV infection. This case history also documents the importance of HIV testing in the diagnostic evaluation of immune-mediated thrombocytopenias.