Urban yellow fever (YF) epidemics have disappeared from Brazil since about 50 years, but a selvatic cycle still exist. In many States, cases are more or less numerous each year. Ae. aegypti was eradicated in 1954, re-appeared temporarily in 1967, and then definitively in 1976-1977. Ae. aegypti is a vector of yellow few (YF), but also of dengue, whose first cases were reported in 1982. Today, dengue is endemic in many regions. A second Flavivirus vector, Aedes albopictus is present since about ten years in some States, from which Säo Paulo. The analysis of the YF cases between 1972 and 1994 allowed us to determine the epidemiologic regions. In the first region, the endemic area, the YF virus is circulating "silently" among monkeys, and the emergence of human cases is rare. In the second region, the epidemic area, some epizootics occur in a more or less cyclic way, and human cases can be numerous. Nevertheless, these outbreaks are considered "selvatic" epidemics, as long as Ae. aegypti is not concerned. From the Amazonian region, the virus moves forward along the forest galleries of the Amazone tributaries, from North to South. Actually, dengue epidemics appear in quite all States, and reflect the geographical distribution of Ae. aegypti. Recently, Ae. aegypti was found in the southern part of the Pará State, in the Carajás region considered to be the source of the main YF epidemics. In another hand, Ae. albopictus is now increasing its distribution area, specially in the suburban zones. The ecology of this potential vector, which seems to have a great adaptative capacity, give this vector an intermediate position between the forest galleries, where the YF virus circulates, and the agglomerations infested with Ae. aegypti. Since a few years, the possibility of urban YF is threatening Brazil, it is more and more predictable and we must survey very carefully the epidemiological situation in some regions of the country.