Introduction - The resurgence of the Rift Valley fever virus (RVFV) epidemic in Kenya in 2006–2007 led to the implementation of animal biological surveillance in Mayotte and the assessment of potential circulation within the population. Methods - RVFV was tested for retrospectively and prospectively in serum samples from patients who sought care between September 1, 2007, and May 31, 2008, for a febrile syndrome at a healthcare facility, and for whom testing for chikungunya, dengue, and malaria was negative. A recent confirmed case was defined by the presence in serum of anti-VFVR IgM (Mac-Elisa) or the VFVR genome (RT-PCR). Results - Of 220 serum samples, 10 (4.5%) were positive: presence of viral RNA (6), IgM (2), or both (2). The onset date of symptoms for the first case was September 27, 2007, and for the last case, May 14, 2008. Seven cases (7/10) occurred between January and April 2008. The patients were aged 16 to 53 years, predominantly men (9/10). No severe cases or deaths were detected. The exposures identified in 9/10 patients were: contact with animal products (5/9), consumption of raw milk alone (1/9), and larval breeding sites in the home alone (3/9). The strains were genetically related to those isolated during the 1997 outbreak in Kenya. Discussion and conclusion - This first recognized indigenous circulation of VFVR in Mayotte illustrates the risk of introduction faced by Mayotte from arboviruses circulating in coastal countries or islands of East Africa. Surveillance efforts should be maintained and strengthened to enable early detection of any outbreak of this virus in Mayotte. (R.A.)