Introduction. An outbreak of chikungunya virus (CHIKV) was reported in the Comoros in early 2005. It subsequently spread to all the islands in the southwestern Indian Ocean, leading to a massive regional outbreak that lasted more than 18 months. In parallel with the enhanced passive surveillance system, additional investigations were conducted to assess the epidemic situation in Mayotte. Methods. A serological survey to determine the prevalence of anti-chikungunya antibodies was conducted using frozen serum samples from pregnant women collected in October 2005 (n=316) and between March and April 2006 (n=629). The community-based clinical survey aimed at measuring the cumulative incidence of suspected chikungunya cases took place between May 1 and 10, 2006 (n=2,235). Results. The survey of serum samples from pregnant women revealed a rate of recent infection (presence of IgM) of 1.6% in October 2005 and 26% in April 2006. The community survey showed a cumulative incidence (from January 1 to May 10, 2006) of clinically suspected chikungunya of 26%. Relative to the population, this corresponds to nearly 250 cases of chikungunya per 1,000 inhabitants between January 2006 and May 2006. Conclusion. These results suggest that the introduction of the chikungunya virus to Mayotte in 2005 led to a massive epidemic in 2006, comparable in scale to that of Réunion. Due to its rapid and widespread spread throughout the region, the development of arbovirus surveillance and prevention programs at the local and regional levels remains of considerable importance for public health. (R.A.)