We here report the results of a programme of AMS dating and stable isotope analysis on human remains from the chambered tomb of Le Déhus, Guernsey. An early use-phase in the range 4100–3900 BC is indicated, confirming the monument's attribution to the Middle Neolithic II as defined in western France. Late Neolithic burial activity is also identified. Stable carbon isotope measurements provide little or no evidence for the consumption of marine foods, although stable nitrogen isotope values are unusually high. These results are situated in the wider context of Neolithic mortuary monuments of the Channel Islands and Normandy.