An epidemiological study has been made of rates of mental illness in a number of ethnic minorities who are immigrants to Britain, and have settled in a denned area of South London. Of the groups considered, those from Africa, the Old Commonwealth, India and Pakistan have the highest rates. The lowest rates were found in those from Cyprus and Malta, native Britons, and those from the Caribbean. After controlling for the effects of age, sex and social class it was found that the pattern of illness in a number of the immigrant groups differed from the pattern found in the native born. Those from Africa, the Caribbean and India and Pakistan manifested an excess of schizophrenia, while those from Eire manifested a dearth of such illness when compared with matched, nativeborn controls. The combination of the following factors was used to try to predict the rank order of illness rates among the ethnic groups considered: community integration; status isolation; status striving in a climate of limited opportunity; and selective migration.