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.