Between June and September 2014, Lower Normandy hosted several large-scale international gatherings, each with its own organizational context and specific, diverse audience, which led local authorities to consult the regional office of the French Institute for Public Health Surveillance (InVS) (Cire) Normandy to assess the health impact of these events and provide data to verify the adequacy of healthcare and emergency response services. Routine health surveillance was supplemented by dedicated health surveillance measures involving several local health stakeholders. During these gatherings, between 215 and 1,635 instances of healthcare utilization were recorded, and no specific health incidents were identified. The evaluation of the effectiveness of the health surveillance systems and tools put in place highlighted the need to develop and adapt a health surveillance system to the specific context of each gathering, particularly with regard to the population involved, the environmental context, and the planned internal healthcare and emergency response capacity. The responsiveness of partners and their active participation in the systems depend on their involvement in planning prior to events and on thorough work to ensure the quality of the data transmitted on a daily basis. Finally, the epidemiological monitoring of potential health events with rapid health impact requires specific healthcare and emergency response needs to be defined in advance.