The incidence of mania in an inner-city area was estimated by both a c
asenote search with later interview and a prospective interview method
. The incidence was found to be twice as high as that in a more rural
area, as estimated by the casenote-based method. Though a high proport
ion of the inner-city population were from ethnic minorities, particul
arly Afro-Caribbean, this could not explain the discrepancy. It is sug
gested that the incidence of mania is related to the mobility of the l
ocal population.