Acute idiopathic thrombocytopenic purpura (ITP) characteristically follows a viral illness in preschool children. The exact role of viruses in the pathogenesis of this disorder remains uncertain, but the finding of markedly elevated levels of platelet-associated IgG serves to distinguish it from the chronic form of the disease and permits speculation on the mechanisms of platelet destruction. Although the spleen is important in both antibody production and platelet destruction, bone marrow synthesis of IgG has also been shown to be increased. The clinical course may be alarming, but mortality is low and prognosis excellent. Controversy has surrounded the role of steroids in the management of acute childhood ITP in retrospective studies. Controlled studies, however, indicate that thrombocytopenia is reversed sooner in treated patients. New assays for platelet-associated IgG offer new insights into this disorder and will allow delineation of acute and chronic disease at the time of diagnosis.