Spontaneous abnormal involuntary movements phenomenologically identical to neuroleptic-induced tardive dyskinesia have been described in schizophrenia for over a century. Because at present nearly all patients with schizophrenia are exposed to neuroleptic medications, information about the prevalence of spontaneous dyskinesia is obtained from accounts from the preneuroleptic era, evaluations of first-episode patients before neuroleptic treatment, and the identification and assessment of drug-naive patients in developing countries. In this report, data from 14 studies of neuroleptic-naive patients with schizophrenia are used to generate age-adjusted estimates of the prevalence of spontaneous dyskinesia. While the precision of this estimate is limited by the difficulty of obtaining large, untreated samples, available data suggest a spontaneous dyskinesia rate of approximately 4% in first-episode schizophrenic patients, 12% for patients ill several years but below age 30 years, 25% for those aged between 30 and 50 years, and 40% for those aged 60 years or older. Relative to the incidence and accrued prevalence of spontaneous dyskinesia expected during the natural history of untreated schizophrenia, the cumulative impact of treatment with new neuroleptic agents has yet to be determined.