Endemic psychosis in western Ireland.

For over 200 years parts of Ireland have been thought to have a high prevalence of psychosis, and recent hospital and community studies have confirmed this impression. In an intensive study of a rural area, the authors found that 4% of the population over age 40 was actively psychotic, with diagnoses of schizophrenia, schizoaffective disorder, and bipolar disorder. Psychosis seems to be endemic in some rural, lower socioeconomic areas in Ireland. Possible etiological explanations are discussed.