Based on sequence analysis of the mitochondrial gene ND4, we determined the presence in Argentina of 3 haplotypes representing different Aedes (Stegomyia) aegypti lineages previously identified in other countries of the Americas, Africa, and Asia. Haplotype 17, the most frequent in Argentina, was previously detected in Brazil. Haplotype 7, restricted in our study to the northwest of Argentina and Bolivia, was formerly found in low frequency in the USA, Brazil, Mexico, and Senegal. Also haplotype 11, belonging to a different haplogroup than the other two, was observed in the present study; it had been reported before in Africa and Asia, but not in the Americas. The coexistence of haplotypes belonging to divergent haplogroups supports the hypothesis of multiple introductions of the species in Argentina.