The southwestern Indian Ocean region faces a constant threat of dengue epidemics. For example, Réunion Island experienced two biologically documented epidemics in 1977–1978 and 2004. Although Réunion has been in an inter-epidemic phase since July 2004, this does not rule out the regular occurrence of sporadic cases or isolated transmission clusters. The epidemiological surveillance system in place detected, between January 1, 2007, and October 5, 2009, five confirmed indigenous cases, five confirmed cases imported from Southeast Asia, and 71 probable cases. The five confirmed indigenous cases all occurred in the municipality of Saint-Louis. On other islands in the southwestern Indian Ocean, several dengue outbreaks have been reported. The importation of the dengue virus by a traveler from Southeast Asia is one of the major risks for an outbreak on the island. The introduction of a new serotype could also lead to the emergence of new and severe clinical forms, including the dengue hemorrhagic fever, which has not yet been reported in Réunion.