The authors report here 2 cases of subacute-onset encephalitis with N-methyl-D-aspartate (NMDA) receptor antibodies. One had a paraneoplastic syndrome associated with a neuroblastoma, whereas the other had no primary tumor. This disease was originally described as a paraneoplastic syndrome in young women with ovarian teratoma. The clinical features of both children resembled the typical symptoms reported for older patients with this disease: psychomotor deterioration, movement disorders, and seizures. One of the reported cases is the first known case of paraneoplastic encephalitis with NMDA antibodies in a child with neuroblastoma. Both cases described here were younger than any of the previously reported cases. Consistent with recently published series, this report suggests that the spectrum of symptoms of encephalitis with NMDA receptor antibodies is probably wider than previously thought.