Opsoclonus-myoclonus syndrome (OMS) is a rare, autoimmune neurological disorder that is poorly recognized and undertreated. Neuroblastoma is found in one half of the cases. Because of the high incidence of spontaneous regression of neuroblastoma, it is unknown whether not finding a tumor means there was none. To define demographic trends and the standard of care in the first large series of OMS, 105 children were recruited over a 13-year period in a retrospective questionnaire survey. Children with and without a tumor differed little in viral-like prodrome and neurological symptoms. Earliest neurological symptoms were staggering and falling, leading to a misdiagnosis of acute cerebellitis. Later symptoms included body jerks, drooling, refusal to walk or sit, speech problems, decreased muscle tone, opsoclonus, and inability to sleep. Tumor resection alone did not provide adequate therapy for most. Adrenocorticotropic hormone (ACTH), prednisone, and intravenous immunoglobulin were used with equal frequency, but ACTH was associated with the best early response. More than one half of the children had relapses. Residual behavioral, language, and cognitive problems occurred in the majority. The delay in diagnosis (11 weeks) and initiation of treatment (17 weeks) is unacceptably long.