SummaryCaptive breeding and re-introduction is integral to the recovery of many threatened species [1], but such practices carry an associated risk of introducing exotic and potentially unknown pathogens into naïve settings. Amphibians are facing a mass extinction crisis and an emerging pathogen, Batrachochytrium dendrobatidis, described only in 1998, is now recognised as a principal driver of these declines [2]. Debate rages about the role of invasion [2,3] versus climate change [4] in determining the distribution of B. dendrobatidis and chytridiomycosis. The severity of the threat from anthropogenic spread is recognized by the recent decision to list chytridiomycosis as a notifiable disease by the OIE (World Organisation for Animal Health) [5]. Case-studies documenting anthropogenic spread are rare, however. Here, we report that native island populations of the IUCN red-listed Mallorcan Midwife Toad Alytes muletensis are infected by B. dendrobatidis and suffering from chytridiomycosis. We trace the source of this infection by screening archived mortalities from a captive-breeding facility that had been used for re-introduction of the species to its native habitat. Our study provides the first strong evidence that the anthropogenic movement of amphibians is spreading B. dendrobatidis; it also provides a salutatory lesson of the need to ensure that breeding-programs are not hot-beds for cross-specific disease transmission, and that species are free of infectious agents prior to re-introduction.