Antibody-mediated encephalopathies associated with serum or cerebrospinal fluid antibodies directed against neuronal structures may present with a multitude of neuropsychiatric syndromes. Although some of the antibody-driven conditions are now well recognized in adults (eg, N-methyl-D-aspartate receptor antibody encephalitis), the spectrum of neuropsychiatric manifestations in the pediatric population is less clear. Psychosis, confusion, catatonia, and additional behavioral changes, along with seizures, encephalopathy, and movement disorders, may be initial manifestations or concurrent features in all age groups. Psychosis, when present, is often part of a broader spectrum of neurological and neuropsychiatric symptoms for which the diagnosis of autoimmune encephalitis is considered. The authors present the case of an adolescent with an acute and isolated psychotic presentation of voltage-gated potassium channel antibody encephalitis, further expanding the phenotypic spectrum of this specific antibody-mediated disease and raising the possibility that specific immune-mediated processes may define a biological subgroup of psychoses.