OBJECTIVE: Analyze clinical, accepted biochemical, physiologic, and socioeconomic risk factors and correlate them with hospital utilization in an elderly population. DESIGN: Prospective, observational study in a defined, randomly recruited population. PARTICIPANTS: 5201 Medicare participants enrolled in the Cardiovascular Health Study (CHS). METHODS: Medicare recipients were randomly assigned to participate in an observational study. Baseline data were compared to hospital admissions and days of hospitalization over four years. DATA ANALYSIS: Data were grouped by type of risk factor and analyzed by Tobit analysis and logistic regression. RESULTS: Baseline variables associated with hospital use (p is less than 0.0001) were history of CHF, stroke, angina, hypertension, ln (timed walk), ln (blocks walked/week), age, gender, and clinic site. Factors not entering the model (p is greater than 0.05) were income, education, smoking, diabetes, weight, dietary fat, marital status, depression, and measures of mental function. CONCLUSIONS: In the elderly, existing health status is the major determinant of hospitalization and overwhelms many classic "risk factors" for morbidity.