On March 19 and 20, 2001, the Institute for Health Surveillance responded to an emergency request from the DGS to conduct an epidemiological investigation at Ernest Hemingway Middle School in Port-en-Bessin, Calvados. The sudden death of a ninth-grade student following a series of health incidents at the school—including students and adults feeling unwell, which led to the school’s closure—added a dramatic dimension to an event that had previously been managed at the local level. The epidemiological investigation allowed for the administration of a face-to-face questionnaire to 84% of students (n=286) and 71% of adults (n=32). The symptoms were dominated by headaches, abdominal pain, nausea, and drowsiness among both students and adults. They occurred in three peaks on March 5, 8, and 15 at the middle school, but episodes also occurred between these dates and outside the school. A large number of students experienced multiple episodes over the 10-day period. Within the school, a few classrooms used for practical work saw the highest number of incidents, but cases of illness were observed in nearly all other areas of the school. Laboratory and radiological tests conducted in the emergency department of Bayeux Hospital did not point to any specific cause. The initial hypothesis was that of environmental poisoning, and multiple tests were conducted, first as an emergency measure and then using more reliable methods by INERIS. The initial results were all negative; however, the tests conducted by INERIS revealed excessively high atmospheric concentrations of volatile organic compounds and acetonitrile in two classrooms. These measurements were confirmed by several samples. However, doubt remains regarding the high concentration of acetonitrile, which could be related to the sampling technique. The results of the various tests conducted as part of the autopsy on the young middle school student confirmed that there was no link between the death and the other events that occurred at the school. Overall, the nature of the symptoms presented by the students and adults, their distribution over time in three episodes of increasing intensity, their recurrence among the same students, the absence of any objective paraclinical signs, and the lack of evidence of environmental exposure at toxic levels or of an infectious source all point to a psychological group phenomenon. However, it is likely that the first episode was triggered by the emission of odors and/or substances from the drainage systems or a workshop, exacerbated by the very poor ventilation of the premises and their extremely high temperatures. The results of the autopsy on the child rule out any link to the events.