Introduction - With the establishment of the Aedes albopictus mosquito in southern France, there is a real risk of initiating a chain of transmission for arboviruses, particularly dengue and chikungunya viruses. Surveillance of cases imported into mainland France and diagnosed by a network of laboratories has been conducted since 2006. This study presents the results for the 2008–2009 period. Methods - A case of dengue or chikungunya is defined by a positive IgM serology or RT-PCR test in a patient sampled in mainland France. Five reference laboratories participate in this network and transmit their data to the InVS. Results - 693 cases of dengue and 86 cases of chikungunya were diagnosed in 2008–2009, with significant monthly fluctuations. The majority of cases reside in Île-de-France and Provence-Alpes-Côte d’Azur.During the vector’s active period (May to November) and in the departments where it is established, the number of dengue cases diagnosed in 2008 and 2009 was 11 and 15, respectively, and the number of chikungunya cases was 7 and 0, respectively. Conclusion - Laboratory surveillance confirms the reality of the risk of introduction of dengue and chikungunya viruses by travelers returning from endemic areas and the relevance of this system in supporting the national anti-spread plan. (R.A.)