Surveillance of listeriosis in France is carried out through mandatory reporting (DO) and the National Reference Center (CNR) for Listeria. Each reported case is interviewed using a specific dietary questionnaire. To improve this surveillance system, additional investigations involving food sampling to detect Listeria monocytogenes (Lm) have been conducted since August 2001 by agents from the Departmental Directorates of Veterinary Services (DDSV) and the Departmental Directorates of Competition, Consumer Affairs, and Fraud Prevention (DDCCRF) at patients’ homes and at the locations where they made their purchases. This article presents the system used to identify the foods responsible for cases of listeriosis and to implement control measures at an early stage. This will help prevent new cases and outbreaks. These investigations were limited to neuromeningeal forms due to their characteristics (shorter incubation period than other forms of listeriosis, higher incidence during outbreaks). A descriptive analysis of the investigations conducted over a 17-month period was performed to assess the contribution of this type of investigation to the prevention of listeriosis.