Between April and July 2004, 32 cases of infantile beriberi were reported in Mayotte, a French overseas collectivity in the Indian Ocean. An investigation team from the French Institute for Public Health Surveillance (International and Tropical Department and the Réunion-Mayotte Interregional Epidemiology Unit) was dispatched to the site. The objectives of this mission were to describe the outbreak and document its mechanisms in order to define emergency public health measures and guide medium- and long-term investigations. This article presents the results of the preliminary descriptive investigation.