Opsoclonus-myoclonus-ataxia syndrome (OMA) in children is most commonly associated with occult neuroblastoma (NB). Although children with OMA and NB have decreased mortality, they suffer from increased neurologic morbidity. The pathogenesis of OMA in NB is not well understood, but current research and treatments support an immune-mediated process. The authors describe an unusual presentation of OMA occurring following 6 months of chemotherapy in a child with stage 4S NB who presented with partial Horner syndrome. Histopathologic examination of his primary cervical tumor showed NB maturation, which may have played a role in precipitating OMA syndrome. Further study of unusual cases of OMA in NB may provide better understanding of the syndrome and additional treatment options for these children.