Intravenous immunoglobulin has been used in the treatment of a variety of disorders since the 1970s. Its safety and efficacy, however, have been evaluated in only a minority of these conditions. At present, intravenous immunoglobulin is licensed for use in primary immunodeficiencies, idiopathic thrombocytopenic purpura, chronic lymphocytic leukemia, Kawasaki syndrome, bone marrow transplantation, and pediatric AIDS. Although considered to be a relatively safe product, it is costly and not without risk of adverse reactions, including transmission of infectious agents. This point has been underscored by the recent report of over 100 cases of hepatitis C infection associated with a commercially available intravenous immunoglobulin preparation. Hepatitis C represents the major risk associated with intravenous immunoglobulin, and physicians must carefully weigh both the risks and benefits of this product before initiating treatment in selected patients.