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Following the establishment of American mink farms outside North America, the species has successfully invaded Europe and South America, and in some places, their presence demonstrably threatens native biodiversity. We surveyed for mink signs along the Andean Patagonian forest in Argentina from 38°52′ S to 54°52′ S, revealing that their range has now expanded to span 800 km of contiguous occupation on the continent including several types of wetlands and has also colonised Tierra del Fuego Island. Rate of expansion was estimated using two methodologies and varied between 5.53 and 9.00 km/year (linear method, large-scale spread) and 4.86 km/year (within a more restricted area, grid method). Diet throughout the region fitted the generalist pattern described for mink elsewhere. Native small mammals were the most frequently consumed category. Crustaceans (patchily distributed in the region) occurred in the diet in proportion to their availability ( r=0.961, p<0.001), but that of waterfowl did not ( r=0.178, p=0.713). Diet was evaluated at one lake throughout a year, revealing that consumption of crustaceans fell in the cold months when bird abundance increased. Based on published work on the impact of American mink as an introduced species in Patagonia and elsewhere, together with our own survey, we discuss the implications of this invasion for biodiversity conservation in Argentinean Patagonia and the associated dilemmas for management policy. [ABSTRACT FROM AUTHOR]