BACKGROUND. Sanofi Pasteur has developed a tetravalent dengue vaccine (TDV) against the world's most common arbovirus infection. METHODS. We assessed the safety and immunogenicity of the TDV in healthy adults randomized into 2 groups. Group 1 received 3 TDV injections at months 0, 4, and 12-15; group 2 received saline placebo at month 0 and then 2 TDV injections at months 4 and 12-15. Adverse events were recorded, and biological parameters and viremia levels were measured. Neutralizing antibodies against 4 World Health Organization (WHO) reference strains were measured before and after vaccinations. RESULTS. A total of 33 participants were enrolled in each group. Demographic characteristics were comparable. No vaccine-related serious adverse event was reported. The most common systemic reactions were headache, malaise, and myalgia. Low viremia levels were detected, mainly of serotype 4. Immune response increased with successive vaccine doses. All participants seroconverted against all 4 serotypes after receiving 3 doses at 0, 4, and 12-15-months, and almost all seroconverted after 2 doses given 8-11 months apart. CONCLUSIONS. Sanofi Pasteur's TDV was well tolerated and induced full seroconversion against all WHO reference strain serotypes after 3 doses.