The primary objective of this study was to assess deepsea food web structure and trophic niches in Baltimore and Norfolk canyons, the adjacent slopes, and chemosynthetic seeps along the mid-Atlantic margin using stable isotope analyses (SIA) and isotope niche width analysis. We hypothesized that the isotopic compositions of canyon versus slope fauna would be distinct, given differences in the physics and chemistry of the canyons and slopes and resulting quality and quantity of the organic matter available to the benthos. These differences should be evident across taxa and among and within feeding groups. We also used SIA to estimate trophic positions of invertebrates and fishes and to examine changes in trophic level with size for specific demersal fish species. Furthermore, comparisons were made between results from SIA for select fishes and stomach content analyses to characterize trophic relationships of fishes over time.