In the 1980s scientists determined that an introduced mountain goat (Oreamnos americanus) population caused negative impacts to subalpine plant communities in Olympic National Park (ONP). These findings resulted in a controversial and costly mountain goat reduction program from 1981–1989. Since 1990 introduced nonnative mountain goats from Montana have successfully colonized Yellowstone National Park (YNP) via the Absaroka and Gallatin mountain ranges. Using systematic aerial surveys from 1997–2001, I documented a breeding goat population inside or within 1 km of YNP that increased from 24 to 96 mountain goats observed (mean observed rate of increase r̄= 0.35). Because of increasing goat populations immediately adjacent to YNP, Montana Fish, Wildlife, and Parks (MFWP) established 2 new hunting districts and 44 mountain goats were harvested near YNP from 1996–2001. The mountain goat is a socially popular “charismatic” species with high watchable-wildlife values. However, within YNP they also are viewed with concern as an exotic species, potentially capable of exploiting fragile subalpine landscapes where, by policy, nonnative ungulates are not welcomed. Based on habitat availability and goat densities to the north, YNP potentially may support 200–300 mountain goats. Important ecological differences between YNP and ONP may reduce the likelihood of negative resource impacts of mountain goats in YNP. However, the speed at which mountain goat numbers and distribution are increasing warrants further habitat and population monitoring to better understand and predict the ecological effects of this new species. Future mountain goat management decisions in YNP should be based on documented impacts of goats on their habitat and other species in YNP and not what has occurred in ONP. Mountain goat management efforts in YNP should acknowledge MFWP's management objective of maintaining viable goat populations in suitable habitats and recognize that goats from Montana will continue to be a source population for future dispersal into and colonization of YNP.