Immunity to yellow fever (YF) is conferred by the interplay of humoral and cellular immune response. Despite the extensive literature on the humoral immune response to the YF vaccine virus, little is known about its cellular immune response to vaccination. The analysis of cytokine production by ex-vivo antigen-stimulated T cells has been considered as a valuable tool for understanding cellular immune response. Thus, we have analyzed two TH1/TH2 signature cytokines (IFN-γ and IL-4) from 12 healthy first-time adults vaccinated with YF17DD virus. The cells, harvested on day 0 (before vaccination) and 7, 15 and 30 days after immunization were antigen-stimulated and analyzed by ELISpot. A significant increase in the number of spot-forming cells during the response to YF 17DD live virus stimulation by ELISpot assay was observed. IFN-γ-and IL-4-producing cells were significantly increased on the 15th day after vaccination in all volunteers. These results presented herein are important for understanding the role of cytokines in the immune response to YF 17DD virus.