An 18-month-old black girl had progressive truncal ataxia, opsoclonus, and multifocal myoclonus associated with a nonresectable abdominal ganglioneuroblastoma. Before chemotherapy, she received intravenously administered IgG, 1 gm/kg, for 2 days; within 48 hours of the first dose, there was significant improvement of the opsoclonus-myoclonus and ataxia. She required a 1 gm/kg maintenance dose every 4 to 6 weeks for a total of 12 doses, but is now free of symptomatic after 2 years with no therapy.