In accordance with the national control program, a standardized epidemiological survey is conducted in all laying hen farms contaminated by Salmonella Enteritidis or Salmonella Typhimurium in France. The survey aims to identify the pathways of introduction and persistence of the bacteria in the farm, in order to guide the management of the outbreak by local veterinary services and stakeholders. However, the information collected in these epidemiological surveys is not centralized and analyzed at the national scale. Ninety-four survey questionnaires on outbreaks that occurred in layer farms in 2020 were collected retrospectively and analysed to determine the main hypotheses on the origin of Salmonella contamination of these farms. Veterinarians conducted the outbreak investigations using standardized questionnaires listing 17 potential sources for Salmonella contamination or persistence in layer farms. The presence of rodents was the most frequent hypothesis of source of contamination, reported in 67% of the outbreaks. Presence of wild birds, other farm animals and breaks in biosecurity measures when entering the poultry house were also reported for one half of the outbreaks, while introduction of Salmonella-infected pullets, persistence of a previous contamination on the farm or rendering trucks were the least reported hypothesis (< 10% of the outbreaks). When asking to rank up to four main hypothesis for Salmonella introduction pathways on the farm, the veterinarians did not conclude for 13% of the outbreaks (12/94). The top-ranking factors were the same as the most reported one: rodents (leading hypothesis for 30% of the outbreaks), other farm animals (14%), wild birds (14%) and breaks in biosecurity (15%). When suspected (9 outbreaks), introduction of Salmonella-infected pullets was considered as the most likely origin of the contamination in 78% of the outbreaks (7/9) because of supporting evidences, as epidemiological information on other outbreaks involving the same pullet provider. Further statistical analysis are currently conducted to identify common patterns in outbreaks taking into account farm characteristics. Recommendations for prevention of outbreaks will be formulated based on the results.