Maintenance is an often overlooked aspect of appraisal. The effective treatment of maintenance within an appraisal is, however, fundamental to informing the decision regarding the optimum investment strategy. This is because the nature of the maintenance strategy can have direct implications on operating costs and other benefits (e.g. travel time savings). As such the impact of maintenance within an appraisal extends far beyond a simple consideration of its financial cost. The first Section of this Note introduces the importance the correct treatment of maintenance has with respect to an economic appraisal. Following Sections present the primary components of maintenance costs, and introduce the notion of whole life costing and the fact that there is a risk that maintenance may not occur. Next, the Note discusses the issues associated with deriving future maintenance costs, and further discuss the need for inclusion within the appraisal of, first, delays to transport users during maintenance works, and second, of the amount of induced and re-assigned traffic. The final Section presents a summary of the key points that should be borne in mind with respect to the treatment of maintenance within an economic appraisal.