Introduction: Surveillance of foodborne illnesses helps guide prevention and control measures for these diseases. Mandatory reporting (MR) of foodborne outbreaks in France showed a significant increase in the number of reported outbreaks between 2005 and 2010. It was necessary to determine whether this increase was real—due to a change in epidemiology that might require control measures—or due to a surveillance bias. Method: To meet the objectives of this study, we analyzed all TIAC outbreaks reported through the mandatory reporting system in France between 1996 and 2010 using a method that, to our knowledge, is innovative, based on statistical models adapted for time-series analysis, in order to quantify the contribution of various characteristics of TIAC occurrence to this increase. Results: The number of foodborne illness outbreaks increased significantly in France between 2006 and 2010, reaching an 116.4% increase in 2009. Salmonella foodborne illness outbreaks, which accounted for 34.2% of outbreaks between 1996 and 2004, did not contribute to this increase. The proportion of the increase attributable to foodborne illness outbreaks where the pathogen was unknown ranged from 48.3% to 63.6% between 2006 and 2010. These outbreaks accounted for 18.7% of all outbreaks between 1996 and 2004. Foodborne illness outbreaks where the implicated food was unknown—26.6% of outbreaks between 1996 and 2004—accounted for 29.2% to 70.2% of the excess between 2006 and 2010. Over the same period, foodborne illness outbreaks in commercial food service establishments, 23.2% of outbreaks during the reference period, accounted for 31.9% to 45.2% of the increase, and outbreaks involving fewer than 3 patients contributed 26.5% to 34.3% of this increase, representing 15.8% of outbreaks between 1996 and 2004. Conclusion: We did not identify any evidence consistent with a significant change in the epidemiology of foodborne illnesses between 2006 and 2010, apart from known factors (in particular a decline in Salmonella cases in France). Several arguments supported the possibility of a surveillance effect explaining the observed increase. The absolute and relative increase in foodborne illnesses occurring in commercial food service establishments would require further study to determine the causes. (R.A.)