This paper reassesses the chronological status of the Lambourn long barrow, which has provided one of the earliest dates from a mortuary monument in Britain. Three new AMS dates on short-lived material indicate that the construction and primary use phase of the monument lies within the period 3760–3645 cal BC, and that the earlier estimate obtained on charcoal (4555–3780 cal BC) is likely subject to the old wood effect, or is residual. This is followed by a consideration of the implications of the new dates in the context of the Mesolithic-Neolithic transition, the timing of which remains poorly understood. It is argued that the evidence is increasingly pointing to a more rapid neolithization process, and that this had implications for the mechanisms involved.