As a consequence of the dengue epidemic in the Bolivian Republic and the northern provinces of Argentina, an outbreak of indigenous dengue occurred for the first time in the Buenos Aires Metropolitan Area. Since January 2009 we assisted imported dengue cases coming from epidemic regions; later, around the end of March, and until middle autumn, indigenous cases appeared. The major concentration of these indigenous cases was in the west area of Buenos Aires City and in the neighboring localities 3 de Febrero and La Matanza. There were several factors that made the local transmission possible: a high vector density, people traveling from epidemic areas and clustering in the geographical zone where the indigenous epidemic occurred, during a period with high medium temperatures, entering 95% of the imported cases during the first days of the viremia. Of the nine patients with alarming signs for the development of severe dengue, seven were indigenous cases with no previous history of dengue infections. We report the clinical and epidemiological findings, and we analyze the factors which regulated the transmission.