The carbon monoxide (CO) poisoning surveillance system tracks the spatial and temporal patterns of reports during the heating season (September 1–March 31). In 2009–2010 and 2010–2011, approximately 1,100 reports were received by the surveillance system during each heating season, with a median of about 34 reports per week. The majority of reports concerned accidental CO poisonings occurring in the home (nearly 9 out of 10 cases), and the two regions most affected were Île-de-France and Nord-Pas-de-Calais, with 194 and 156 reports in 2010–2011 (190 and 175 reports, respectively, in 2009–2010). Regardless of the heating season considered, the increase of more than 50% in the weekly number of incidents corresponded to periods of orange alerts for snow and ice or extreme cold. In collaboration with Météo-France, prevention messages regarding the risk of CO poisoning were incorporated into the alert maps. Given the influence of certain weather phenomena (extreme cold, snow and ice, and high winds), it would be beneficial to implement local prevention measures as soon as high-risk weather events are forecast. (R.A.)