Background: Influenza is a major cause of illness, disruption to daily life, and work absenteeism among healthy working adults aged between 18 and 64 years. This group is not included among the traditional priority groups for annual vaccination. Immunization rates remain low. Objective: To assess the economic implications of a strategy for annual vaccination of this group. Methods: Using the societal perspective, this cost-benefit analysis included the direct and indirect costs associated with vaccination as well as the direct and indirect costs prevented by vaccination. Clinical and economic variable estimates were derived primarily from the published literature. For this model, it was assumed that vaccination occurred in efficient, low-cost settings such as at the work site. Monte Carlo simulation was used to calculate the mean net costs or savings along with the 95% probability interval, and sensitivity analyses explored the sensitivity of the cost model to different values of the input variables. Results: Vaccinating healthy working adults was on average cost saving, with mean savings of $13.66 per person vaccinated (95% probability interval: net savings of $32.97 to net costs of $2.18), with vaccination generating net savings 95% of the time. The model was most sensitive to the influenza illness rate, the work absenteeism rate due to influenza, and hourly wages. In the worst-case scenario vaccination was not cost saving. Vaccination also generated net costs to society during years with a poor vaccine - circulating virus strain match. In all of the other sensitivity analysis scenarios, vaccination was cost saving. Conclusion: Influenza vaccination of healthy working adults on average is cost saving. These findings support a strategy of routine, annual vaccination for this group, especially when vaccination occurs in efficient and low-cost sites.