On January 30, 2006, a mass illness incident occurred among a choir of teenagers gathered in a municipal hall in Pamproux, in the Deux-Sèvres department. Called to the scene following two reports of people feeling unwell, emergency responders suspected carbon monoxide (CO) poisoning. An investigation was conducted to describe the cases, identify the cause of the symptoms, and, if applicable, the environmental source responsible for these symptoms. A case was defined as a person reporting symptoms on January 30 or 31 based on a questionnaire completed by everyone present in the hall during the events. The environmental investigation sought to identify possible sources of poisoning. Among the 169 people interviewed, 113 reported at least one symptom (headache: 80% and abdominal pain: 58%). The 23 hospitalized cases, all choir members, showed no abnormal levels of CO in their blood. Among the choir members, being female was associated with reporting symptoms (RR=1.6, 95% CI [1.1; 2.6]). The environmental investigation did not identify a source of poisoning. The investigation did not confirm the hypothesis of CO poisoning. However, it did highlight characteristics typically observed in episodes of psychogenic syndromes. (R.A.)