Human listeriosis is a foodborne infection caused by Listeria monocytogenes (Lm). Between March 10 and April 2, 2014, five cases of Lm infection belonging to PCR group IIa and the rare AscI/ApaI 210408-150807bis PFGE profile were identified by the National Listeria Reference Center. An investigation was launched to determine the source of contamination and guide control measures. A case was defined as an infection with Lm of PCR group IIa and PFGE profile AscI/ApaI 210408-150807bis, diagnosed in France between January 28 and August 18, 2014. The dietary history of the cases was collected using a standardized questionnaire. A traceability investigation and an inspection of the implicated establishment, including food and environmental sampling, were conducted. Eleven cases were identified in 5 regions. An establishment in Franche-Comté was identified as the likely source of contamination: among the 10 cases interviewed, 6 reported having purchased and consumed food from this establishment. No common food item was identified. The inspection of the establishment revealed multiple hygiene deficiencies. Food and environmental samples confirmed the presence of Lm strains with the same microbiological characteristics as the human strains. The hypothesis of widespread and prolonged environmental contamination of the establishment was accepted to explain this outbreak. The establishment was closed on July 3, 2014, for thorough cleaning and disinfection. Products purchased before July 3, 2014, were recalled, and clearance testing was conducted on food items sold after the establishment reopened. No contaminated products were identified after reopening, and no new cases were reported.