Death rates during a period of rapid deinstitutionalization of a state mental hospital population showed consistent reductions that were statistically significant in the elderly patient population 65 years and older. These reductions were most marked for deaths due to pneumonia; there was a moderate decrease in cardiac deaths, and essentially no change in cancer death rates. The findings suggest that through a variety of mechanisms deinstitutionalization may have had a beneficial effect on the mortality of elderly patients who remained hospitalized. Moreover, the resultant increased need for beds for these patients dramatizes the importance for program planners to base their projections for hospital use on a continuing analysis of trends rather than on static data.