Persicaria extremiorientalis is native to Japan, the Russian Far East, China, and Korea. It is documented here with specimens from the Atlantic coastal region including the states of Connecticut, New York, New Jersey, Maryland and North Carolina. The earliest collections in North America are from Queens, New York in 1961. The species belongs to Persicaria section Persicaria, and is distinguished from all other North American species by the combination of stems usually hispid or sparsely pilose with long, soft hairs; ocrea outer surfaces strigose and the apices setose; leaf blades eglandular and the abaxial surfaces golden-strigose; racemes dense, often nodding, the bracts short-ciliate; achenes small, brown, lenticular or biconcave (rarely trigonous) and basally tumescent. The existence of this species in North America is substantiated with herbarium specimens and a full description and an identification key to it and related species are provided.