A survey of the prevalency of patients with mental illness who were under treatment in New Haven was analyzed according to religion, national origin, and immigrational status. It was found that psychoneurotic disorders were more frequent among Jews whereas the rate of affective disorder in this group had fallen to the average of the population. Alcoholism is most prevalent among the Irish Catholics. There has been a general fall in the rate of organic mental disease, particularly in that of general paresis among Negroes. The illness of senescence and the affective illnesses are higher in the foreign-born while psychoneurotic disorders are more frequent in the native-born. Schizophrenia and psychosis with mental deficiency are not related to the social variables.Comparisons were made between these findings and previous studies. Speculative explanations are offered to explain the trends and disproportions.