OBJECTIVES: The purpose of this study is to estimate the 5-year budget impact of a pneumococcal vaccination program of population aged 65-year-old in Spain. METHODS: A dynamic model based on differential equations was built for the conceptualization of the disease and the parameters were populated with the vaccine efficacy data coming from the CAPITA clinical trial of the 13-valent pneumococcal conjugate vaccine (PCV13). If S stands for susceptible, I for infective, V shows the number of individuals who are effectively vaccinated at each time and t is the time variable and the parameters beta and gamma show the transmission and natural recovery coefficients respectively, the differential equation of the model is: dS(t)/dt=-β*I(t)*S(t)+γ*I(t)-V(t) and dI(t)/dt=+β*I(t)*S(t)-γ*I(t). Program duration was fixed to 5 years, and every year the 65-year cohort would be vaccinated (coverage of 49.3%). Economic parameters included hospital costs of treating pneumonias, meningitis, bacteremia, and empyema as well as the outpatient costs of treating pneumonia in the community (41.5% of the cases). Costs sources were official databases for hospitalizations and vaccine, and a local study for outpatient costs of pneumonia. Mortality rates related to pneumococcal infections reported in the UK are applied to the Spanish case. RESULTS: In 5 years-period with a 65 year old cohort of 513,000 people, the vaccination program is expected to avoid about 35,700 cases of pneumococcal disease (the majority of them otherwise causing pneumonia), and about 1,419 related deaths. Vaccination costs of 59.5 million euros would be completely offset by medical cost reduction of 124 million euros, yielding to a net saving of 64.5 million euros. CONCLUSIONS: PCV13 vaccination targeting the cohort of 65 year-old Spanish adults is expected to result in net savings for the health care system in addition to significant cases of pneumonia avoided and related health improvements for the patients.