On February 11, 2000, a physician from the student health promotion department (school physician) reported a suspected outbreak of foodborne illness at a vocational high school to the Pas-de-Calais Departmental Directorate of Health and Social Affairs. This school has 239 students divided into 12 classes. One hundred and seven students are part-time boarders (78 girls and 29 boys) and eat lunch in two consecutive sittings at 11:45 a.m. and 1:00 p.m. The school cafeteria does not serve any other groups. On February 7, seven students who had eaten at the cafeteria presented with “allergy-like” symptoms, leading the school nurse to suspect histamine poisoning. On February 8 and 9, five other students exhibited similar symptoms. The results of the investigations (descriptive and case-control) conducted before the students left for vacation to determine the cause of the outbreak and propose corrective and preventive measures are presented in this article.