The diet of Antarctic toothfish (Dissostichus mawsoni) and Patagonian toothfish (D. eleginoides) was examined around the south sandwich islands in the southern ocean, one of few regions with overlapping populations of the two species. Despite large differences in the proportion of stomachs containing prey (76.2 % of D. mawsoni compared to 7.2 % of D. eleginoides), diet composition was broadly similar (schoener overlap index of 74.4 % based on prey mass) with finfish (particularly macrourids and muraenolepidids) and cephalopods (mainly Kondakovia longimana) comprising more than 90 % of the prey mass of both species. Predation rates of the main fish prey, as mean counts per stomach sampled, were spatially correlated with their relative abundance around the islands derived from fishery bycatch data, suggesting a general lack of prey selectivity. This study supports the view that bathyal toothfish are opportunistic carnivores and finds that D. mawsoni and D. eleginoides occupy a similar trophic niche and are likely to compete for prey in regions where both are distributed. However, the large increase in rate of prey occurrence and size of prey in D. mawsoni stomachs relative to D. eleginoides suggests species differences in feeding behaviour, which may reflect the increased metabolic demands of a cold water-adapted physiology.