The use of acute-care hospitals by the elderly is rising rapidly, particularly in the age group 75 and older. Any changes that will reduce the length of stay could result in considerable savings in health care costs. It is imperative to look at present policies and explore possible changes that could reduce costs by reducing the total hospital days. A study was conducted in a 290-bed county-founded community hospital in California that serves the majority of disadvantaged and poor elderly residing in an area with a population of approximately 300,000 persons. The objective was to determine what demographic, medical, and sociologic characteristics of elderly patients recorded at admission would be of value in predicting those most likely to change their functional status. It was found that the most important predictors of deterioration of function are (1) older age, especially 85+, and (2) abnormal mental status. Patients admitted from nursing homes had a longer than average length of stay, and those who survived (80 per cent) returned to a nursing home. It was concluded that routine assessment of elderly patients admitted for acute illness or injury could facilitate discharge planning by an early prediction of the level of care that will be required after discharge. This assessment should include preadmission mental and functional status; identification of causes for, and correction of, acute confusional states; and an assessment of the impact of the present illness or injury on future level of function following rehabilitation. This could result in a reduced length of average hospital stay.