We studied the incidence, associated morbidity, and impact on health care charges of neurologic complications in 38 children with acute immune thrombocytopenic purpura (ITP) treated with intravenously administered IgG. Thirteen patients (34%) had transient neurologic complications, manifested by severe headache, nausea, and, rarely, aseptic meningitis. Computed tomography was performed in nine patients. Twelve patients were hospitalized longer than was required for their ITP alone. Neurologic complications caused by the IgG preparations used in the treatment of childhood ITP occur more frequently than has previously been suggested and may substantially increase the cost of treatment.