In Ontario, Canada, a mass vaccination strategy was developed and implemented to mitigate the effects of the 2009 pandemic influenza A (pH1N1). This study investigated its cost-effectiveness, mirroring actual events in Ontario, compared to no vaccine strategy. From a societal perspective, 1,780,491 cases and 154 deaths were averted through vaccine administration; the incremental cost effectiveness ratio predicted that the vaccination program saved $117 per case avoided, or $1.35 million per death averted, for total savings of $208.3 million. From a government perspective (Ontario Ministry of Health and Long Term Care) this strategy required an expenditure of $28 per case averted and $0.33 million per death averted, for a total cost of $252.4 million.