Introduction - On August 29, 2008, the National Reference Center for Salmonella reported four recent isolates of Salmonella Putten, a rare serotype, from laboratories in northwestern France. An investigation was conducted to identify the source of contamination. Method - Individuals with a Salmonella Putten isolate between July 15 and September 15 (confirmed cases) and symptomatic individuals in their social circle (probable cases) were interviewed via telephone questionnaire. Results - Nine cases were identified, including one probable case, occurring between July 25 and August 10 and involving individuals who had stayed in four departments in the northwest. Two cases were hospitalized. All cases had consumed fresh ground beef patties, most of which were undercooked and purchased primarily from the same retail chain supplied by a food processing facility in the west. Salmonella Putten contamination was identified in two batches of ground beef patties and ground beef produced on July 24 and August 6. Conclusion - This outbreak confirms the significant role of undercooked ground beef in the occurrence of salmonellosis and the need to cook meat thoroughly, particularly for at-risk individuals. (R.A.)