This paper reports the first set of isotopic data relating to human diet from the Samoan Archipelago. Carbon and nitrogen stable isotope data measured on bone collagen were used to assess dietary patterns of prehistoric communities on Tutuila Island, American Samoa. We examined 14 human bones from three sites dated to three distinct periods: ~1,000 years ago (N = 5); -500 years ago (N = 8) and -150 years ago (N = 1). The isotopie data suggest that the human diet on Tutuila over the last 1,000 years was composed mainly of terrestrial resources with some consumption of coastal reef products. These data suggest a possible dietary change over time, with a higher dependence on marine resources in the earlier period shifting to a more terrestrial diet in the later period. Several possibilities for this dietary shift are suggested including: change in community specialization; marine resource depression; disintensification of marine procurement; intensification of horticultural production; and cultural or social changes in resource allocation.