In a 3-year, randomized, controlled, open-label phase III trial enrolling 3707 adults aged > or = 60 years we evaluated whether the immunogenicity of an intradermal trivalent inactivated seasonal influenza vaccine, containing 15 microg of haemagglutinin per strain per 0.1 ml dose, is superior to that of a conventional intramuscular vaccine. Intradermal vaccine was given using an intradermal microinjection system. After the first vaccination, both vaccines satisfied the immunogenicity criteria for influenza vaccines for older adults set out in European regulatory guidelines, and geometric mean haemagglutination inhibition antibody titers and seroprotection rates were higher (statistically superior) with intradermal vaccination. Higher immune responses with intradermal vaccine were also observed after the 2nd and 3rd annual vaccinations. Both vaccines were well tolerated with similar systemic reactogenicity profiles. This intradermal influenza vaccine for older adults is a beneficial option for influenza protection, consistently enhancing antibody responses without compromising safety.