Abstract Cold air incursions over subtropical South America are the precursor conditions for frost, a recognized extreme thermal weather event affecting plant growth damaging agricultural production over the whole Argentinian territory. Given that sub-freezing temperatures occurring during the active growing season may harm the cambium tissues and their daughter cells, frost injury can be recorded in annual tree rings in the form of anatomical anomalies. For this study, six forest sites of Araucaria araucana, a multi-centennial tree species, from NW Patagonia were considered. From 321 trees, 1374 frost injuries in the growth rings, named frost rings, were identified and their calendar dating allowed the development of a regional chronology of frost rings covering the period AD 1256 to AD 1993 (738 yrs.). This represents the longest record at present of extreme low thermal events for Patagonia. Frost injuries were mostly restricted to the middle section of the growth rings, suggesting the incidence of late spring frosts. Moreover, frost rings were observed mainly in the juvenile portions (