Guilty but insane: the insanity defence in Ireland, 1850-1995.

Background: This is a retrospective study describing sociodemographic and clinical characteristics of an almost complete sample of insanity acquittees in Ireland between 1850-1995.

Method: Case records and legal files were examined for each of the 437 patients admitted to the Central Mental Hospital under guilty but insane criteria, and a profile of sociodemographic, forensic and clinical data completed in each.

Results: The number of insanity acquittees has fallen five-fold since the 19th century. Acquittees were usually single males from rural areas, aged in their 30s, who had committed a violent crime while suffering from a major psychiatric illness. Female insanity acquittees were relatively few in number and were equally likely to have been charged with violent crime, especially against their own children. The mean length of detention was 14.5 years.

Conclusions: The insanity defence is rarely used in Ireland, is largely confined to serious offences (especially homicide), and generally results in prolonged detention.