This is a study of the relationship between variations, over time, in mental hospital admissions, and concommitant variations in economic conditions. The research hypothesis is that during economically depressed periods mental hospital admissions increase and during economically prosperous periods they decrease. Theoretically, it is a study of a relationship between changes over time in the structure of the economy and changes in the distribution of mental illness in a population. We find that fluctuations in mental hospital admissions show strong inverse correlations with fluctuations in the employment index in New York State over the period 1910 to 1960. The data reveal, however, that subgroups among the hospitalized population exhibit grossly different patterns of reaction to economic changes. In fact, without segregating the population of admissions according to differential risk of exposure to stress during economic changes, it may not be possible to observe this relationship, For reasons not yet well understood, risk of exposure to economic stress appears to vary with diagnostic category of illness and socioeconomic status.