Stable carbon and nitrogen isotope analyses of human skeletal remains from several sites in southernmost Chile and Argentina provide data on prehistoric human subsistence adaptations in this region. The combination of carbon isotope ratios in bone collagen, bone apatite, and tooth enamel, and nitrogen isotope ratios in collagen are used to identify the relative dietary contributions of terrestrial C3 and C4 plant and animal foods as well as freshwater and marine resources. The stable isotope data are interpreted in conjunction with other dietary evidence to explain geographic and chronological variations in hunter-gatherer subsistence adaptations in southern Patagonia.