In October 2015, in accordance with the recommendations of the assessment mission on the healthcare system for migrants living in the Calais camp, an epidemiological surveillance system was established by Santé publique France. Due to a new influx of migrants, the system was expanded to the Grande-Synthe camp in December 2015. The objectives of the surveillance were to detect any outbreaks early and to monitor trends in target diseases in order to adapt the provision of curative and preventive care. A review of the literature and consultation among the scientific departments of Santé publique France helped define the priority diseases. Surveillance was based on strengthening the existing reporting system to the Hauts-de-France Regional Health Agency and on syndromic surveillance using data transmitted by healthcare facilities managed by hospitals and nongovernmental organizations. During the study period, the majority of healthcare visits were for infectious diseases, particularly acute lower and upper respiratory infections, influenza-like illnesses, and scabies. Several outbreaks were detected in the Calais camp: an influenza A(H1N1) outbreak, a measles outbreak, and a chickenpox outbreak, which led to vaccination campaigns. This experience demonstrated the feasibility and usefulness of syndromic surveillance in the complex context of an open migrant camp, where the resident population is constantly changing and where healthcare provision, involving multiple providers, evolves regularly.