The safety and immunogenicity of a monovalent inactivated vaccine against Leptospira interrogans serogroup Icterohaemorrhagiae was evaluated in 84 volunteers according to the route of administration, i.e., subcutaneous (SC) or intramuscular (IM), in a double-blind randomised trial. The volunteers were randomised into four groups: SC vaccine; IM vaccine; SC placebo; and IM placebo. Primary vaccination comprised two injections on day 0 and day 14, with a booster after 6 months. A second booster was given 30 months after primary vaccination. Local reactions within 1 h of injections were rare, with no difference between vaccine groups. Local reactions within 3 h were more frequent after the second, third and fourth SC injections than after IM injections. Systemic reactions never occurred within 1 h of vaccination and were rare within 3 days; the rates were comparable for the different vaccine groups. Evolution of the antibody responses, as assessed by microscopic agglutination tests and specific IgG and IgM ELISAs, were similar for both injection routes. IgG seroconversion rates after the first booster were 97% (95% CI 80-100%) for the SC vaccine group, and 96% (95% CI 80-100%) for the IM vaccine group, and both reached 100% for IgG after the second booster. The safety and immunogenicity of the anti-leptospiral vaccine were both good. Monitoring of antibody levels established that a booster dose triggered a strong antibody response in fully vaccinated subjects at 30 months after primary vaccination.