Anti-personnel landmines are one of the main causes of civilian victimization in conflict-affected areas and a significant obstacle for post-war reconstruction. Demining campaigns are therefore a promising policy instrument to promote long-term development. We argue that the economic and social effects of demining are not unambiguously positive. Demining may have unintended negative consequences if it takes place while conflicts are ongoing, or if they do not lead to full clearance. Using highly disaggregated data on demining operations in Colombia from 2004 to 2019, and exploiting the staggered fashion of demining activity, we find that post-conflict humanitarian demining increases economic activity and students’ performance in test scores, especially in areas with better market access. In contrast, economic activity does not react to post-conflict demining events carried out during military operations, and it decreases if demining takes place while the conflict is ongoing. Rather, demining events that result from military operations are more likely to exacerbate extractive activities and promote deforestation.