This paper presents and discusses the results of a palaeodietary and AMS dating study of burials from the Mesolithic sites of Téviec and Hoëdic, Brittany, France. In common with other Mesolithic coastal populations in Europe, isotopic analysis demonstrates the significant use of marine resources by the sites' inhabitants. Greater interest, however, is provided by the inter- and intrasite details of the analysis. There is an unexpected difference between the two sites, with the inhabitants of Hoëdic deriving 70 to 80% of their protein from the sea, while the inhabitants of Téviec appear to show a more balanced use of marine and terrestrial protein. At the intrasite level, women, and particularly young women, were found to exhibit less use of marine foods. It is suggested that this could indicate an exogamous, patrilocal marriage pattern, with some women marrying in from more inland communities. The AMS dating program shows that the sites were roughly contemporaneous but were used for burial over a longer period of time than originally anticipated. Two cases could suggest the reuse of graves after the passage of centuries, a practice more typically associated with Neolithic passage graves. Unresolved issues remain surrounding the calibration of the dates, complicated by the inclusion of marine protein in the diet, but even before correction for this effect a number of dates overlap with the earliest Neolithic of the region. This raises a number of possible scenarios for the Mesolithic-Neolithic transition in Brittany.