Objective: The aim of this multicenter study is to investigate risk factors for unplanned hospitalizations, including individual and environmental factors, notably air pollution. Classifying at risk patients might help preventing unplanned hospitalization of oldest old. Correlations between medical data and the atmospheric pollution modelling will allow us to enhance the forecast system with dose-effect functions. Validation of a multi dimensional standardised instrument (InterRAI-MDS) will help in the development of a shared medical record.