Every year, the Tour de France attracts between 12 and 15 million spectators along the roads of France to watch the riders pass by during the 21 stages. Spectators spend an average of 6 hours on the roadside cheering on the riders. For its 100th edition, the Tour de France passed through Lower Normandy on July 10, 2013. A 33-kilometer time trial took place, starting in Avranches and finishing at Mont-Saint-Michel (a major French heritage site). Given the short distance of the stage and the site’s international renown, a large number of people were expected for this stage, particularly at the finish line. This concentration of a large number of people in the same place at the same time can lead to increased health risks, thereby requiring enhanced health surveillance. During the summer months, these risks may be exacerbated by weather conditions. The Normandy Regional Health Agency had therefore stepped up epidemiological surveillance before, during, and after the event (July 8–11), focusing on the emergency departments of hospitals near the event.