This paper is a study of diet and subsistence among Mesolithic and Early Neolithic populations in the Iron Gates section of the Danube Valley, with emphasis on the sites of Lepenski Vir and Vlasac in Serbia and Schela Cladovei in Romania. The first part of the paper reviews the evidence of animal and plant residues and human skeletal indicators; the second presents new data from stable isotopic analyses of human bone supported by AMS 14C dates. Isotopic and dental evidence suggest that Mesolithic people prior to 7600 BP had high protein diets in which the bulk of the protein was derived from riverine food sources. Significant differences are evident between the isotopic signals of Mesolithic males and females buried at Vlasac and Lepenski Vir, indicating differences in overall diet. These differences are most easily explained in terms of movement of individuals between groups, linked to the practice of local group exogamy. A shift in dietary pattern occurred at Lepenski Vir between ca 7600 and 7300 BP. The bone chemistry of individuals post-dating 7300 BP reflects the intake of significantly higher proportions of terrestrial foods. This change may reflect the introduction of stock-raising and/or cultivation in the Iron Gates. If so, then the transition from Late Mesolithic to Neolithic at Lepenski Vir was not characterised by a wholesale shift in subsistence from foraging to farming; the earliest Neolithic inhabitants of the site continued to obtain a significant proportion of their dietary protein from riverine resources. The wider implications of the AMS dates and stable isotopic data are also considered.