Headwater streams are critical, fragile ecosystems that supply food and nutrients for an array of organisms that are vital to the overall health of a stream. As the dominant vertebrates in headwater streams of the southern Appalachian Mountains, plethodontid salamanders are critical to healthy headwater communities. However, a neglected feature of these ecosystems is the community of parasites that infect salamanders. The digenetic trematode Metagonimoides oregonensis uses the aquatic snail Elimia proxima as its first intermediate host and the plethodontid salamander Desmognathus amphileucus as its second intermediate host. In a series of southern Appalachian streams, we tested the hypothesis that variance in the prevalence and intensity of infection in salamander hosts is related to respective densities of the snail and salamander species. Infection prevalence was 100% across all streams. There was a strong relationship between the density of the snail host and infection-intensity level in the salamander host. However, the relationship with salamander density was not important, a finding that conflicts with the results of parasitological studies involving lentic and marine systems. The influence of this trematode on the ecology of headwater streams and the resident salamanders has been underappreciated, and a number of aspects of this relationship remain unknown.