Aim of study. To describe the emergence of dengue 3 virus in Côte d'Ivoire during a yellow fever outbreak which occurred in 2008. Materials and methods. Sera from suspected cases of yellow fever as well as contacts of yellow fever confirmed cases and imported dengue fever cases were tested for immunoglobulin M (IgM) anti-yellow fever virus and anti-dengue virus (for IgM antibodies to yellow fever and dengue viruses) and by a specific real time RT-PCR (Bio-Rad) for yellow fever virus and dengue virus viral RNA detection. Results. Of the 511 sera from suspected cases of yellow fever tested, 21 (4.1%) were confirmed positive for yellow fever virus antibody, while 33 (7.6%) of the 432 sera tested were positive for dengue virus antibody. Thirteen viremic subjects, one for yellow fever virus and 12 for dengue 3 virus, were detected by RT-PCR. The majority of the confirmed cases of yellow fever (85%) and dengue 3 fever (93%) were adults, and resided in the city of Abidjan and its regions. Conclusion. These results indicate the existence of transmission foci of these arboviruses diseases in Côte d'Ivoire and the essential contribution of molecular tests for their diagnosis.