Scores of arboviroses have been indexed in Brazil with variable rates of morbidity and mortality. Emergence of arboviroses and their transmission by hematophageous vectors are closely related to the country's recent history and in particular to its economic, social and ecological development. Most arboviroses are caused by alphaviruses and flaviviruses. Some species of bunyavirus are also found. Brazil is often regarded as an arbovirus sanctuary where dormant or nonpathogenic viruses can find an optimal context to emerge or reinforce their pathogenic potential in the middle term. Currently yellow fever and especially dengue fever are major public health problems.