An economic evaluation of reducing the age threshold for routine influenza vaccination in Spain from 65 to 50 years was performed. A probabilistic model was used to compare a policy based on a recommendation to vaccinate all adults aged 50-64 with the existing vaccination policy for that age group, during interpandemic periods. Two perspectives were considered: third-party payer (TPP) and societal. Model inputs were obtained primarily from the published literature and validated through expert opinion. From TPP perspective, incremental cost-effectiveness ratios were estimated at euro14,919 per quality-adjusted life-year (QALY) gained and euro9731 per life-year gained. From societal perspective, the corresponding results were euro4149 per QALY and euro2706 per life-year gained. Extending routine influenza vaccination to people over 50 years of age is likely to be cost-effective.