OBJECTIVES: Influenza disease may result in a severe disease causing hospitalization and deaths in younger children and older adults. Early antiviral treatment may improve clinical outcomes. Our goal was to estimate the oseltamivir cost-effectiveness in the prevention of pneumonia due to influenza in the Colombian children and elderly population. METHODS: A probabilistic decision-tree model to simulate Influenza-Like Syndrome (ILS) burden of disease and influenza pneumonia complications in Colombian population was programmed in excel. Transition probabilities and care costs for Colombia were obtained from a literature review and surveillance databases. Oseltamivir effectiveness was meta-analyzed from randomized trials and observational studies. Incremental cost-effectiveness ratio (ICER) for oseltamivir in the prevention of pneumonia complication in population under five years of age and older than 65 year old with ILS was estimated. Monte Carlo simulation with 10,000 iterations were used to estimate 95% confidence interval. Costs were expressed in 2013 USD. RESULTS: A total of 275,788 ILS cases in children and 86,675 in elderly population were estimated for 2014. Whit no oseltamivir would occur 75,789 and 62,817 pneumonias in children and elderly, respectively, and a total 22,719 deaths. Including the oseltamivir treatment at 90% coverage would avert 33,462 pneumonias and 6639 pneumonia deaths. The oseltamivir cost were estimated on US$ 6,419,552, and it would be a cost-saving intervention in population younger than 5 years old and equal or older than 65 years old with an ICER of US$ -953 (IC95% US$-934 to -759). CONCLUSIONS: The use of oseltamivir in children and elderly whit ILS appear to be a cost-saving strategy in Colombia, to prevent pneumonia and death complications, when it is administrated between 48 hours of symptoms onset.