This paper concerns the difficulty of taking long-term effects on health into account in an economic valuation. Indeed, public decision makers should incorporate the cessation lag between implementation of an abatement policy and achievement of all of the expected mortality-related benefits for any projects involving health impacts. This paper shows how this time lag problem can be handled by proposing two approaches—either in terms of deaths avoided or of life years saved—within a dynamic perspective. The main findings are that long-term health benefits calculated by standard methods and widely applied to adverse health effects should be corrected downwards when incorporated into an economic analysis. The magnitude of correction depends on the discount rate, on technical choices dealing with epidemiology and on the method chosen to assess mortality benefits.