In March 1999, the InVS published the initial results of the Air & Health Surveillance Program – 9 Cities (PSAS-9). This first phase demonstrated the feasibility of bringing together various stakeholders in the fields of air pollution and health to address a common issue. The results also allowed for the conclusion that associations exist between daily variations in all urban air pollution indicators and total daily mortality, as well as cardiovascular and respiratory mortality, thereby reinforcing, based on French data, the scientific knowledge in this field. Today, we are publishing in this report the results of the second phase of PSAS-9, which focused primarily on estimating short-term exposure-risk relationships between pollution indicators and hospital admission indicators. This second phase also confirmed the results of Phase I regarding the short-term impact of air pollution on mortality through longer study periods. In addition, exploratory analyses using new indicators and sensitivity analyses on the robustness of the results were conducted. Finally, methodological tools were developed to optimize data collection and statistical modeling. All of these results enabled the quantification of the short-term health impact of air pollution in the nine cities of the PSAS-9. The PSAS-9 is now a sustainable system for the epidemiological monitoring of the impact of urban air pollution on health, designed to provide useful information to decision-makers and the public. (R.A.)