Tardive dyskinesia is thought to result from neostriatal dopaminergic receptor supersensitivity induced by chronic treatment with neuroleptics. Similarly, receptor supersensitivity occurring in other dopaminergic regions of the brain could result in the development of supersensitivity psychosis. As with tardive dyskinesia, severe forms of the disorder are rare. Ten such cases are described whose main characteristic is that psychotic symptoms can no longer be masked by increased dosages of neuroleptics. Diagnostic criteria for the disorder are proposed, and treatment with antiepileptic medication is described.