Bethlem's Irish: migration and distress in nineteenth-century London.

Association between migration and mental illness is widely reported. This study aimed to gain insight into the mental health of Irish migrants into Britain in the years 1843-53. Casebooks from the period were examined for Irish ethnicity, and clinical profiles were compared with those of age-matched control samples. Irish-born patients were found to have a greater proportion of diagnoses of mania than controls (p < or = 0.01). They were more likely to be admitted for 12 months or longer (p < or = 0.001) and more likely to receive religious attributions for illnesses by the treating physician. The more common diagnosis of mania in the Irish group can be explained in terms of the effects of migration, differences in idioms of distress, or in terms of prejudice.