Illegal economic activities are not only associated with higher levels of violent crime, they may also increase unforeseen risks and cause other negative unintended consequences for populations. This paper investigates the causal effects of illegal gold mining on malaria incidence. For this purpose, I employ unique Colombian satellite data with the location of illegal gold mines matched to municipal governmental health reports on the number of malaria cases. To identify causal effects, I use preexisting geochemical gold anomalies as an instrumental variable for illegal gold production. I find positive and large effects of illegal gold mining on malaria incidence. My estimates suggest that when an area containing illegal gold mines increases by 1 hectare, the annual parasite index for malaria increases by 1.04 cases per 100,000 inhabitants.