Introduction - On the night of February 23–24, 2006, an outbreak of acute gastroenteritis (AGE) was identified at the Arc 1800 ski resort in Bourg-Saint-Maurice. Epidemiological and environmental investigations concluded that contamination of the drinking water supply was the source of the outbreak. Materials and Methods - An analysis of reimbursements for anti-diarrheal medications was conducted using data from the French National Health Insurance (AM) to assess the ability of these data to describe the health impact of this outbreak by comparing them with data from the field epidemiological investigation. Results - The AM data enabled the plotting of an epidemic curve similar in shape to that derived from the field survey, although the number of GEA cases from the AM data was lower than that from the field survey during the epidemic peak. Analysis of geographic information revealed that the outbreak was confined to the city’s tourist district and reinforced the hypothesis of a waterborne origin linked to contamination of the water supply system. Conclusion - The method used enables the retrospective detection of GEA outbreaks. Geographic data enable the localization of cases based on the water supply system affected by contamination and the distinction between local cases and tourist cases. The restriction of cases to only those requiring medical care and the delays in obtaining data are the main limitations to the use of surveillance data. (R.A)