On October 6, 2011, emergency and medical services responded to a middle school in Saint-Sauveur-le-Vicomte (50) after a student at the school experienced a vasovagal episode and an increasing number of children began exhibiting nonspecific neurological and/or gastrointestinal symptoms throughout the morning. About thirty children were transported to the emergency departments of the Cherbourg and Saint-Lô hospitals. No medical diagnosis could be made, and no environmental abnormalities were identified that could explain the event. At the request of the Basse-Normandie Regional Health Agency (ARS), an investigation was conducted by the Normandy Regional Health Agency (Cire Normandie). The results of the investigation led to a diagnosis of psychogenic mass psychosis. The investigation also identified the triggering factor: the onset of a vagal episode in one student, followed by a psychosomatic episode in a second student who witnessed the index case’s episode. The intervention of emergency and medical services likely played a significant role in amplifying the phenomenon. Unexplained mass psychogenic illness is a relatively unknown emerging phenomenon in France. Consequently, these events pose challenges in terms of care and management for the services likely to encounter them. The Cire Normandie recommends that information regarding unexplained collective syndromes be disseminated as widely as possible to emergency and healthcare services, so that they are able to make an early diagnosis and implement appropriate care for these situations. (R.A.)