As part of the implementation of an epidemiological surveillance program for RATP employees, a study of mortality among RATP staff was conducted in collaboration with the InVS. The objective was to describe the causes of death in this population, identify any excess risks, and examine associations between mortality risks, occupational characteristics, and exposure to certain hazards. This report covers the first phase of the study, namely the comparison of observed mortality among RATP employees with that of the general population in the Île-de-France region. The analyses included nearly 70,000 employees who worked for at least one year at RATP between 1980 and 1999, among whom 5,130 deaths occurred (including after retirement). It was observed that their mortality rate is lower than that of the general population in the Île-de-France region, which is a classic characteristic of large occupational cohorts, who are on average in better health than the general population of the same age. There is thus a significant under-mortality from cancer of 10% among men and 14% among women. A significant excess of deaths from ischemic heart disease is observed among men, however, but cannot be further interpreted in the absence of specific analyses based on occupational characteristics. The analysis of causes of death by socio-occupational categories, occupations, and exposure to certain occupational factors will constitute the second phase of the analysis and will begin shortly. It will allow for a more specific examination of potential risks among these workers and their possible links to working conditions. These results will also be published by the RATP and the InVS in a joint report. (R.A.)