Ofatumumab is a fully human anti-CD20 monoclonal antibody in phase II-III trials for various autoimmune and lymphoreticular diseases. We used it to treat a rituximab-allergic child with severe, chronic-relapsing, opsoclonus-myoclonus syndrome (OMS), characterized by persistent cerebrospinal fluid (CSF) B-cell expansion and T-cell dysregulation. He had relapsed despite chemotherapy, plasma exchange with immunoadsorption, and resection of ganglioneuroblastoma, detected 3 years after OMS onset. The four ofatumumab infusions (1,195 mg/m(2) total dose) were well tolerated, and CSF B-cell expansion was eliminated. No further relapses have occurred in 3 years, but he remains on low-dose ACTH with neuropsychiatric residuals of OMS.