We read with interest the article by Klaas and colleagues1 on adult-onset opsoclonus-myoclonus syndrome (OMS). The authors reported the clinical characteristics of 21 patients at the Mayo Clinic and 116 patients in the literature, and they found 2 patients2,3 with adult-onset OMS associated with anti– N-methyl-D-aspartate receptor antibodies in their literature review. Initial symptoms of these 2 patients were behavioral and/or mood changes, and they developed severe encephalopathy.