Baltinglass is a multi-chamber Neolithic passage tomb in Co. Wicklow, Ireland, excavated in the 1930s. This paper presents the results of a radiocarbon dating programme on charred wheat grains and hazelnut shell found underlying the cairn, and on cremated human bone found within and near two of the monument’s five chambers. The results are surprising, in that three of the six determinations on calcined bone pre-date by one or two centuries the charred cereals and hazelnut shells sealed under the cairn, dating to c. 3600–3400 cal bc. Of the remaining three bone results, one is coeval with the charred plant remains, while the final two can be placed in the period 3300/3200–2900 cal bc, that is more traditionally associated with developed passage tombs. A suggested sequence of construction is presented beginning with a simple tomb lacking a cairn, followed by a burning event – perhaps a ritual preparation of the ground – involving the deposition of cereal grains and other materials, very rapidly and intentionally sealed under a layer of clay, in turn followed by at least two phases involving the construction of more substantial chambers and associated cairns. What was already a complex funerary monument has proven to be even more complex, with a history spanning at least six centuries.