Between 30% and 60% of older patients experience functional decline after hospitalization, resulting in a decline in health-related quality of life and autonomy. This is associated with increased risk of readmission, nursing home placement and mortality, increased length of hospital stay and increased need for health care at home. A decreased functional status is a risk factor for the development of geriatric syndromes such as pressure ulcers, falls, delirium, incontinence and further functional decline. Functional decline is mostly defined as a decline in performing the activities of daily living (ADL) and/or instrumental activities of daily living (IADL). This functional decline is not necessarily related to the medical reason for the hospital admission but to the pre-admission health status and the iatrogenic effects of hospitalization. Effective and efficient hospital care for older patients starts with the identification of patients who are at risk for the development of functional decline. Therefore, the aim of this thesis was: To determine a prediction model to identify older patients at risk for functional decline after hospitalization that is easy to use in clinical practice as a first step in the prevention of a loss of function and independence. Functional decline was defined as a decline of at least one point on the Katz ADL index (six items: bathing, dressing, toileting, transferring, eating and the use of incontinence materials) at three months after admission compared to premorbid ADL status. One literature study and four prospective cohort studies (total n=1628) were conducted to develop and validate this prediction model. In the cohort studies the premorbid functional status was measured within 48 hours after admission by interview; patients were asked to describe the situation two weeks prior to admission to eliminate possible effects of the illness causing hospital admission. At follow up, three months after admission, functional status was measured again by telephone interview. This thesis describes the development of a prediction model to identify older patients at risk for functional decline after hospitalization in patients 65 years and older acutely admitted to the general internal wards of three hospitals. The AUC was 0.71, the Hosmer Lemeshow test showed P-value 0.95 indicating a good fitting model. The model was validated in an independent population of internal medicine patients and a population of cardiac surgery patients (both ? 65 years). A scorecard, Identification of Seniors At Risk–Hospitalized Patients (ISAR-HP), was developed based on this model. At threshold 2 (score ?2 indicating high risk for functional decline) the sensitivity, specificity and positive and negative predictive value were 87%, 39%, 43% and 85%, respectively. Pre-admission need for assistance in IADL, use of a walking device, need for assistance in traveling, and no education after age 14 are the predictors of a model to identify older patients at risk for functional decline following hospital admission. This thesis also describes an the implementation of the results of this research into clinical practice, showing how the results of our studies can contribute to safe and targeted care for older hospitalized patients.