Some arboviruses are highly pathogenic for Men or animals. Arboviruses epidemiological patterns in Madagascar were determined by entomological, serological, and virological surveys. We listed potentials arboviruses vectors in Madagascar. Entomological results generated by us during five years, as well as prior to, are shown. We caught more than 150,000 hematophagous arthropods, belonging to 107 species at least. 3 of these species were new. 4183 inoculation pools were done. We studied serollogically (by HI test) samples collected from 563 animals and 626 Men. Our data, in agreement with others collected from 1965 to 1982, demonstrate that arboviruses circulate in the whole island. Positive reactions were obtained mainly with Flavivirus, in particular with West-Nile. Nine various arboviruses, including dengue-2 virus isolated from an individual having travelled to La Reunion, have been isolated. Dakar-Bat and Mengo virus have been observed. We studied transmission cycles of the following viruses: Babanki, West-Nile, Rift Valley Fever, Crimean-Congo Hemorrhagic Fever, MMP 158, Ngari, Perinet and Andasibe; the last 2 being endemics. In relation to Madagascar biogeographic characteristics (long-term isolation, scarce communications, high endemicity, and low vertebrate density), we evaluated the risk of potential introduction and amplification of various arboviruses (dengue, yellow fever, japanese encephalitis, Sindbis and Chikungunya). The risk is very high for dengue due to the presence of susceptible mosquitoes strains while the virus circulates in East Africa and in the Indian Ocean area. This risk seems to be very low for yellow fever, and intermediate for other arboviruses.