As the French territories closest to the areas initially affected by the 2009 A(H1N1) influenza pandemic, the regions of Guadeloupe, French Guiana, and Martinique, along with the communities of Saint Martin and Saint Barthélemy, had to rapidly establish an appropriate epidemiological surveillance system to monitor the emergence of this new strain of influenza. Following a containment phase focused on individual case detection and management, surveillance was implemented in the general population, primarily based on data from sentinel physician networks and virological confirmations. Since the available information varied across the different territories, the number of cases caused by the A(H1N1)2009 virus was estimated using two distinct methods. The five territories experienced an epidemic linked to the A(H1N1)2009 virus, as did all countries in the Caribbean region. This epidemic took hold between early August and mid-September 2009 in four territories; the last, Saint-Barthélemy, was not affected until the end of the year. Estimates of attack rates, which remain below 8% regardless of the territory or the estimation method used, suggest that a new wave of the epidemic is a possibility, especially since vaccination rates are very low in these territories. (R.A.)