Abstract: Objectives Cannabis is a popular drug in Flanders, in spite of the fact that the prevention of its use lists high on the Flemish political agenda. The Flemish Government aims to prevent cannabis use efficiently and in achieving this, a health economic analysis could be helpful. The possibilities and limitations of applying economic evaluation techniques to the prevention of substance (ab)use, are discussed in this paper. Methods A thorough literature search, interviews with key persons, an internet search and an analysis of unpublished reports and documents was performed. Results The interrelation between various forms of substance use, and of the array of strategies to prevent this (including the costs thereof), seems to demand a joint evaluation of multiple substances. Conclusions More than methodological difficulties, the general lack of knowledge on age- and time-specific health and income effects caused by various forms of substance (ab)use, currently makes the evidence-based evaluation of prevention of cannabis use in Flanders a virtually impossible undertaking.