This report supplements a number of others which are designed to note the incidence of mental disorders and diseases from the standpoint of 'interregional differences in the institutionalization of mental patients in the United States'. The statistics are carefully compiled and the conclusions drawn from them are conservatively stated. It is obvious that since ninety-seven per cent of all hospitalized mental patients in the United States are taken care of in public institutions, and since approximately one per cent of the total population is hospitalized because of a mental handicap, the problem constitutes one of the most important units in the field of public health.