The cultural transition from Mousterian to Aurignacian is abrupt at l'Arbreda Cave and occurs within a homogeneous sedimentary unit with no visible lithologic changes. Fragments of milligram-size charcoal were collected immediately above and below the cultural boundary for radiocarbon dating by accelerator. Four charcoal fragments from the lowest basal Aurignacian level yielded dates of 37, 700±1,000, 37,700±1,000, 39,900±1,200, and 38, 700±1,200 BP (average 38,500±1,000 BP). These ages are similar to three dates from the same cultural horizon at El Castillo Cave in Cantabria and both sets of dates are significantly older than the earliest reported for the Aurignacian in the Aquitaine and in other parts of Central and Western Europe. The dates are in accord with similarly early dates for Aurignacian in Bulgaria and suggest that appearance of Aurignacian peoples is synchronous across Europe. Three fragments from the uppermost Mousterian level yielded dates of 39, 400±1,400, 34,100±750, and 41,400±1,600 BP. Discounting the spurious 34, 100 BP result, these dates are slightly older (average 40,400±1, 400 BP) but overlap the basal Aurignacian dates. The data show that the transition from Mousterian to Aurignacian was chronologically abrupt at this location. These results strongly support the replacement hypothesis.