Unintended consequences are recognised as a potential risk for well-intentioned social marketing interventions and as a comparatively under-researched topic in the field. This case study uses an intervention tackling deliberate grassfires to explore the application of social marketing in a novel context, its potential effectiveness in demarketing antisocial behaviours and the potential of such interventions to generate positive and negative unintended consequences. The intervention’s evaluation confirms social marketing’s potential value in tackling ingrained antisocial behaviours within communities. It also revealed unexpected benefits accruing from changes within the target community, within the sponsoring fire service and in the relationship between the two. The paper concludes by discussing the implications of potential unexpected and unplanned consequences for intervention planning, conduct and evaluation
