Background Knowledge of the long term effects of air pollution on human health has been improving over the last ten years, mainly as a result of efforts to design and carry out large scale epidemiological studies. Notwithstanding this, no long term data are available for Mediterranean countries, where higher air temperature, particles’ composition and Saharan dust all influence environmental characteristics – making these countries different to continental and northern European areas. In previous short-term effect studies in Europe, a clear north-south gradient in the particulate matter (PM-10) mortality association was observed, with the Mediterranean cities showing higher relative risks than continental cities. Better knowledge of the long term effects of air pollutants, including fine and coarse particles, is needed to contribute to policy on the environment and health, to update and support EU legislation in this field, to plan mitigation actions and to implement effective, practical measures. Objectives The LIFE MED-HISS project is a demonstration project involving partners in Spain, France, Italy and Slovenia. Its main objectives are: To update and develop EU environmental policy and legislation with improved data on the adverse health effect of air pollution (PM10, PM2.5, NO2 and O3); To consolidate the knowledge base for the development, assessment, monitoring and evaluation of environmental policy and legislation, by setting up a European surveillance system of long term effects of air pollution; To assess the feasibility of the adopted approach in other European countries. Expected results: An evaluation of the long term effects of PM10, PM2.5, NO2 and O3 on mortality and hospitalisation, considering natural causes, cancers, cardiovascular and respiratory diseases and asthma; An evaluation of the Health Impact Assessment (HIA) of air pollution in four EU countries – Italy, France, Slovenia and Spain (Catalonia); The creation of guidelines, a database and a report describing different exposure assessment experiences in the four European countries, with an assessment of inter-country variations; An evaluation of the feasibility of a simplified hybrid approach for air pollution exposure estimation, which could be used in future epidemiological studies.