Thirty 500-900 year-old specimens of Northern White Cedar, Thuja occidentalis, were discovered growing on xeric rock outcrops in the Quebec boreal forest, seven more than 700 years old. The oldest has an 869-year tree-ring sequence and an estimated germination age exceeding 900 years; this makes them among the oldest individuals for the species thus far noted in the literature. Such long tree-ring series offer great potential to extend the dendrochronological record in eastern Canada.