Introduction - Since July 2004, Réunion has been in an inter-epidemic phase for dengue but remains at risk of a resurgence of the disease, necessitating rigorous epidemiological surveillance to detect arbovirus transmission clusters at an early stage. Method - During the inter-epidemic period, surveillance for dengue (a notifiable disease since 2006) was strengthened by a biological surveillance system based on laboratory reporting of borderline or positive IgM results, positive RT-PCR tests, and dengue virus isolations. Results - In 2007, 26 probable cases and 2 confirmed cases of dengue were identified in Réunion, all of which were autochthonous. Seven cases (25%) were hospitalized. No cases of dengue hemorrhagic fever or deaths were reported. The male-to-female ratio was 1.33, and the mean age was 36.5 years [9–80]. A single cluster was identified between May and June 2007 in the municipality of Saint-Louis (3 probable cases and 2 confirmed cases (DEN-1: n=1)). Only five spontaneous mandatory reports were received by the Regional Directorate of Health and Social Affairs. Discussion - The biological surveillance of dengue implemented in Réunion since 2006 appears to be the most appropriate method of epidemiological surveillance during the inter-epidemic period. The identification in 2007 of a DEN-1 virus strain homologous to the one that circulated in 2004 would suggest indigenous viral transmission of the DEN-1 serotype in Réunion in an endemic-epidemic pattern, with sporadic cases occurring during inter-epidemic periods. The introduction of a new serotype by a traveler could have serious consequences, such as a new epidemic, the emergence of hemorrhagic clinical forms, or even deaths. (R.A.)