The aim of this study is to describe the colonization by the Aedes aegypti in the region. A survey carried out in 1985 detected the species in São José do Rio Preto. The mosquito has spread and reached the 30 countries of the region till 1988. In the district and rural areas, the first vector focus was found out in 1987 in one of the 29 districts and rural areas, having spread to the others till 1991. The foci have been mainly identified through larval researches in locations with a great concentration of containers, and the greatest occurrence of larvae of Aedes aegypti has been in tires, the most frequent means of spread. The foci have been mainly identified between November and April, periods of greater incidence of rains. The delimits of foci showed that the containers which were mostly infested by the mosquito in homes have been tires and vases of plants. The most important consequence of the presence of Aedes aegypti has been the occurrence of dengue epidemics.