In 1998, during a radiation survey of a building that had housed a sales office for a company manufacturing items containing radium, the OPRI detected dose rates of several μSv/h in the building’s basement. Since 1978, this building had housed a daycare center, whose occupants may thus have been exposed to ionizing radiation both externally and likely internally (through radon inhalation, and the ingestion and inhalation of radium dust). However, the results of another analysis campaign conducted by the OPRI in the spring of 2000 indicate normal radon levels within the building’s premises and the absence of radium dust on the surfaces examined. This situation resulted from the installation in 1993 of a coating designed to protect occupants from radon emissions and potential contact with radium dust. From that date onward, the dose received by occupants therefore stemmed solely from external radiation. In a letter dated June 2, 2000, the Institute for Public Health Surveillance (InVS) was commissioned by the DGS to assess the feasibility of conducting an epidemiological study to evaluate the potential effects of exposure to ionizing radiation among children who attended the daycare center.