The purpose of this study was to increase our understanding of the bioaccumulation of mercury in northern two-lined salamanders (Eurycea bislineata bislineata) in freshwater stream ecosystems. We collected 111 adults and 131 larval northern two-lined salamanders from six streams in Garrett County, Maryland. These salamanders were collected in April, July, and September 2010. We measured the size and tissue mercury content in all of these salamanders. We also measured the total and methyl mercury concentrations in stream water on monthly basis from April through December 2010. Averaged over all stream ecosystems, adult northern two-lined salamanders had significantly greater total mercury concentrations than larval salamanders (29.6 vs. 23.8 ng g-1). For individual stream ecosystems, the mean tissue mercury contents in adult northern two-lined salamanders were significantly greater than the mean tissue mercury contents in larval northern two-lined salamanders for Bear Pen and Mill Run. Adult and larval salamanders from the Little Savage River and Mud Lick had 1.5-2 times greater mean tissue mercury contents than salamanders in all other streams. These two streams also had significantly greater total and methyl mercury concentrations. Despite their different life-stage feeding behaviors (terrestrial vs. aquatic), the tissue mercury contents of adult (r = 0.76) and larval (r = 0.79) northern two-lined salamanders were strongly linked to the methyl mercury concentrations in stream water. This implies that northern two-lined salamanders may be a useful bioindicator of mercury pollution in relatively pristine stream ecosystems.