Schizophrenia and mental handicap: an historical review, with implications for further research.

The relationship between schizophrenia and 'mental handicap' has been obscured by historical changes and varying diagnostic criteria. It has been generally accepted that there is an increased incidence of psychotic illness among people with intellectual retardation, but detailed community surveys are limited. Catatonia, severity of illness and research potential are all to be found in this 'dual diagnosis' group. The value of an historical analysis is underlined.